4. Long-Term Debt

Long-term debt consists of the following:

Senior Secured Credit Facility

On March 9, 2011, the Company entered into a senior secured credit facility, or the 2011 Credit Facility, which initially consisted of a $700.0 million revolving credit facility, or the 2011 Revolving Credit Facility, with a syndicate of financial institutions as lenders. The 2011 Credit Facility was subsequently amended on July 26, 2012 to include a $500.0 million term loan, or the 2011 Term Loan, with a syndicate of financial institutions as lenders. On May 4, 2015, the Company amended the 2011 Credit Facility to extend the maturity date of the 2011 Revolving Credit Facility by one year to March 9, 2017. The 2011 Term Loan matured on March 9, 2016 and the $229.7 million outstanding was repaid in full. Prior to its termination, the 2011 Term Loan most recently bore interest at either LIBOR plus the applicable margin between 2.00% and 3.00% or the base rate plus the applicable margin between 1.00% and 2.00%, based on the Company’s consolidated leverage ratio. The Company terminated the 2011 Revolving Credit Facility on February 15, 2017 and the $410.0 million outstanding was repaid in full. Prior to its termination, the 2011 Revolving Credit Facility most recently bore interest at either LIBOR plus the applicable margin between 4.00% and 5.00% or the base rate plus the applicable margin between 3.00% and 4.00%, based on the Company’s consolidated leverage ratio.

On February 15, 2017, the Company entered into a $1,450.0 million senior secured credit facility, or the 2017 Credit Facility, consisting of a $1,300.0 million term loan B, or the 2017 Term Loan B, and a $150.0 million revolving credit facility, or the 2017 Revolving Credit Facility, with a syndicate of financial institutions as lenders. The 2017 Revolving Credit Facility was to mature on February 15, 2022 and the 2017 Term Loan B was to mature on February 15, 2023. The 2017 Credit Facility was amended, effective March 16, 2018, to make certain technical amendments in connection with the offering of the 2024 Convertible Notes, as defined below. The Company terminated the 2017 Credit Facility on August 16, 2018 and the $1,178.1 million outstanding was repaid in full. Prior to its termination, the 2017 Term Loan B most recently bore interest at either the eurocurrency rate plus a margin of 5.50% or the base rate plus a margin of 4.50%, and the 2017 Revolving Credit Facility most recently bore interest at either the eurocurrency rate plus a margin of either 4.50% or 4.75% or the base rate plus a margin of either 3.50% or 3.75%, based on the Company’s consolidated leverage ratio. The eurocurrency rate was based on adjusted LIBOR and was subject to a floor of 0.75%. The base rate represented the highest of the Federal Funds Rate plus 0.50%, one-month adjusted LIBOR plus 1.00%, and the prime rate set by Credit Suisse, and was subject to a floor of 1.75%.

The 2017 Term Loan B was issued to the lenders at a 2% discount, or $26.0 million. The Company incurred approximately $22.6 million of debt issuance costs in connection with the 2017 Credit Facility. The debt issuance costs and the discount were recorded on the Company’s consolidated balance sheet and were being amortized over the life of the 2017 Credit Facility using the effective-interest method. The Company wrote off all remaining unamortized debt issuance costs and discount related to the 2017 Credit Facility upon its termination, which is included in the loss on extinguishment as described below.

On August 16, 2018, the Company entered into a new $1.25 billion senior secured credit facility, or the 2018 Credit Facility, consisting of a $250.0 million term loan A, or the 2018 Term Loan A, a $750.0 million term loan B, or the 2018 Term Loan B, and a $250.0 million revolving credit facility, or the 2018 Revolving Credit Facility. The 2018 Term Loan A and 2018 Revolving Credit Facility both mature on August 16, 2023 and the 2018 Term Loan B matures on August 18, 2025. However, the 2018 Term Loan A and 2018 Revolving Credit Facility will both mature on February 14, 2019 if the outstanding principal on the 2019 Convertible Notes, as defined below, exceeds $350.0 million and the Company exceeds certain leverage ratios on such date. In addition, the 2018 Term Loan B will mature on either: (i) May 16, 2019 if the outstanding principal on the 2019 Convertible Notes, as defined below, exceeds $350.0 million and the Company exceeds certain leverage ratios on such date; or (ii) December 15, 2023 if the outstanding principal on the 2024 Convertible Notes, as defined below, exceeds $350.0 million and the Company exceeds certain leverage ratios on such date. The Company did not exceed those certain leverage ratios as of February 14, 2019 and as such, the 2018 Term Loan A and 2018 Revolving Credit Facility will continue to mature on August 16, 2023. All obligations under the 2018 Credit Facility are unconditionally guaranteed by certain direct and indirect wholly-owned subsidiaries of Herbalife Nutrition Ltd. and secured by the equity interests of certain of Herbalife Nutrition Ltd.’s subsidiaries and substantially all of the assets of the domestic loan parties. Also on August 16, 2018, the Company issued $400 million aggregate principal amount of senior unsecured notes, or 2026 Notes as described below, and used the proceeds from the 2018 Credit Facility and the 2026 Notes to repay in full the $1,178.1 million outstanding under the 2017 Credit Facility. For accounting purposes, pursuant to FASB ASC Topic 470, Debt, or ASC 470, these transactions were accounted for as an extinguishment of the 2017 Credit Facility. The Company recognized a loss on extinguishment of $35.4 million as a result, which is recorded in other expense (income), net within the Company’s consolidated statement of income for the year ended December 31, 2018.

The 2018 Term Loan B was issued to the lenders at a 0.25% discount, or $1.9 million. The Company incurred approximately $11.7 million of debt issuance costs in connection with the 2018 Credit Facility. The discount and debt issuance costs are recorded on the Company’s consolidated balance sheet and are being amortized over the life of the 2018 Credit Facility using the effective-interest method.

Borrowings under both the 2018 Term Loan A and 2018 Revolving Credit Facility bear interest at either the eurocurrency rate plus a margin of 3.00% or the base rate plus a margin of 2.00%. Borrowings under the 2018 Term Loan B bear interest at either the eurocurrency rate plus a margin of 3.25% or the base rate plus a margin of 2.25%. The eurocurrency rate is based on adjusted LIBOR. The base rate represents the highest of the Federal Funds Rate plus 0.50%, one-month adjusted LIBOR plus 1.00%, and the prime rate quoted by The Wall Street Journal, and is subject to a floor of 1.00%. The Company is required to pay a commitment fee on the 2018 Revolving Credit Facility of 0.50% per annum on the undrawn portion of the 2018 Revolving Credit Facility. Interest is due at least quarterly on amounts outstanding under the 2018 Credit Facility.

The 2018 Credit Facility requires the Company to comply with a leverage ratio. The 2018 Credit Facility also contains affirmative and negative covenants customary for financings of this type, including, among other things, limitations or prohibitions on repurchasing common shares, declaring and paying dividends and other distributions, redeeming and repurchasing certain other indebtedness, loans and investments, additional indebtedness, liens, mergers, asset sales and transactions with affiliates. In addition, the 2018 Credit Facility contains customary events of default. As of December 31, 2018 and 2017, the Company was in compliance with its debt covenants under the 2018 Credit Facility and 2017 Credit Facility, respectively.

The 2018 Term Loan A and 2018 Term Loan B are payable in consecutive quarterly installments which began on December 31, 2018. In addition, beginning in 2020, the Company may be required to make mandatory prepayments towards the 2018 Term Loan B based on the Company’s consolidated leverage ratio and annual excess cash flows as defined under the terms of the 2018 Credit Facility. The Company is also permitted to make voluntary prepayments. On or prior to February 16, 2019, amounts voluntarily prepaid under the 2018 Term Loan A and 2018 Term Loan B will incur a prepayment premium of 1%; thereafter, amounts outstanding under the 2018 Term Loan A and 2018 Term Loan B may be voluntarily prepaid without premium or penalty, subject to customary breakage fees in connection with the prepayment of a eurocurrency loan. These prepayments, if any, will be applied against remaining quarterly installments owed under the 2018 Term Loan A and 2018 Term Loan B in order of maturity with the remaining principal due upon maturity, unless directed otherwise by the Company.

As of December 31, 2018 and 2017, the weighted-average interest rate for borrowings under the 2018 Credit Facility and 2017 Credit Facility was 6.80% and 6.79%, respectively.

During the year ended December 31, 2018, the Company borrowed an aggregate amount of $1,000.0 million under the 2018 Credit Facility and repaid a total amount of $1,231.9 million, including $5.0 million on amounts outstanding under the 2018 Credit Facility and $1,226.9 million to repay in full amounts outstanding under the 2017 Credit Facility. During the year ended December 31, 2017, the Company borrowed an aggregate amount of $1,300.0 million under the 2017 Credit Facility and repaid a total amount of $483.1 million, including $73.1 million on amounts outstanding under the 2017 Credit Facility and $410.0 million to repay in full amounts outstanding under the 2011 Credit Facility. During the year ended December 31, 2016, the Company borrowed an aggregate amount of $200.0 million and repaid a total amount of $429.7 million on amounts outstanding under the 2011 Credit Facility. As of December 31, 2018 and 2017, the U.S. dollar amount outstanding under the 2018 Credit Facility and 2017 Credit Facility was $995.0 million and $1,226.9 million, respectively. Of the $995.0 million outstanding under the 2018 Credit Facility as of December 31, 2018, $246.9 million was outstanding under the 2018 Term Loan A and $748.1 million was outstanding under the 2018 Term Loan B. Of the $1,226.9 million outstanding under the 2017 Credit Facility as of December 31, 2017, $1,226.9 million was outstanding under the 2017 Term Loan B. There were no borrowings outstanding under the 2018 Revolving Credit Facility and 2017 Revolving Credit Facility as of December 31, 2018 and 2017, respectively. There were no outstanding foreign currency borrowings as of December 31, 2018 and 2017 under the 2018 Credit Facility and 2017 Credit Facility, respectively.

During the year ended December 31, 2018, the Company recognized $83.6 million of interest expense relating to the 2018 Credit Facility and 2017 Credit Facility, which included $2.9 million relating to non-cash interest expense relating to the debt discount and $3.2 million relating to amortization of debt issuance costs. During the year ended December 31, 2017, the Company recognized $87.0 million of interest expense relating to the 2017 Credit Facility and 2011 Credit Facility, which included $4.2 million relating to non-cash interest expense relating to the debt discount and $4.4 million relating to amortization of debt issuance costs. During the year ended December 31, 2016, the Company recognized $24.1 million of interest expense relating to the 2011 Credit Facility, which included $4.1 million relating to amortization of debt issuance costs.

The fair value of the outstanding borrowings on the 2018 Term Loan A is determined by utilizing over-the-counter market quotes for similar instruments, which are considered Level 2 inputs as described in Note 12, Fair Value Measurements. As of December 31, 2018, the carrying value of the 2018 Term Loan A was $245.4 million and the fair value was approximately $240.7 million. The fair values of the outstanding borrowings under the 2018 Term Loan B and the 2017 Term Loan B are determined by utilizing over-the-counter market quotes, which are considered Level 2 inputs as described in Note 12, Fair Value Measurements. As of December 31, 2018 and 2017, the carrying amount of the 2018 Term Loan B and 2017 Term Loan B was $738.2 million and $1,190.2 million, respectively, and the fair value was approximately $729.3 million and $1,226.1 million, respectively.

Convertible Senior Notes due 2019

During February 2014, the Company initially issued $1 billion aggregate principal amount of convertible senior notes, or the 2019 Convertible Notes, in a private offering to qualified institutional buyers, pursuant to Rule 144A under the Securities Act of 1933, as amended. The Company granted an option to the initial purchasers to purchase up to an additional $150 million aggregate principal amount of 2019 Convertible Notes which was subsequently exercised in full during February 2014, resulting in a total issuance of $1.15 billion aggregate principal amount of 2019 Convertible Notes. The 2019 Convertible Notes are senior unsecured obligations which rank effectively subordinate to any of the Company’s existing and future secured indebtedness, including amounts outstanding under the 2018 Credit Facility, to the extent of the value of the assets securing such indebtedness. The 2019 Convertible Notes pay interest at a rate of 2.00% per annum payable semiannually in arrears on February 15 and August 15 of each year, beginning on August 15, 2014. The 2019 Convertible Notes mature on August 15, 2019, unless earlier repurchased or converted. The Company may not redeem the 2019 Convertible Notes prior to their stated maturity date. Holders of the 2019 Convertible Notes may convert their notes at their option under the following circumstances: (i) during any calendar quarter commencing after the calendar quarter ending March 31, 2014, if the last reported sale price of the Company’s common shares for at least 20 trading days (whether or not consecutive) in a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter exceeds 130% of the conversion price for the 2019 Convertible Notes on each applicable trading day; (ii) during the five business-day period immediately after any five consecutive trading day period, or the measurement period, in which the trading price per $1,000 principal amount of 2019 Convertible Notes for each trading day of that measurement period was less than 98% of the product of the last reported sale price of the Company’s common shares and the conversion rate for the 2019 Convertible Notes for each such day; or (iii) upon the occurrence of specified corporate events. On and after May 15, 2019, holders may convert their 2019 Convertible Notes at any time, regardless of the foregoing circumstances. Upon conversion, the 2019 Convertible Notes will be settled in cash and, if applicable, the Company’s common shares, based on the applicable conversion rate at such time. The 2019 Convertible Notes had an initial conversion rate of 23.1816 common shares per $1,000 principal amount of the 2019 Convertible Notes, or an initial conversion price of approximately $43.14 per common share, based on the retroactive adjustment due to the Company’s two-for-one stock split described in Note 2, Basis of Presentation. The conversion rate is subject to adjustment upon the occurrence of certain events and was 23.2245 common shares per $1,000 principal amount of the 2019 Convertible Notes, or a conversion price of approximately $43.06 per common share, as of December 31, 2018. As of December 31, 2018, the if-converted value of the 2019 Convertible Notes exceeded their outstanding principal amount by $249.1 million since the closing price of the Company's common shares was $58.95 compared to the conversion price of $43.06. The Company has entered into capped call transactions with respect to its common shares, which are expected generally to reduce the potential dilution upon conversion of the 2019 Convertible Notes in the event that the market price of the common shares is greater than the strike price of the capped call transactions. See Note 8, Shareholders’ Deficit, for additional discussion on the capped call transactions.

During the fourth quarter of 2018, the last reported sale price of the Company’s common shares exceeded 130% of the conversion price for the 2019 Convertible Notes for at least 20 trading days in the period of 30 consecutive trading days ending on, and including, the last trading day of the quarter. As such, the 2019 Convertible Notes will be convertible at the holders’ option during the first quarter of 2019. The Company will reclassify the difference between the aggregate principal amount and the carrying value of the 2019 Convertible Notes of approximately $18.6 million from additional paid-in capital to temporary equity on its consolidated balance sheet on January 1, 2019.

The Company incurred approximately $26.6 million of issuance costs during the first quarter of 2014 relating to the issuance of the 2019 Convertible Notes. Of the $26.6 million issuance costs incurred, $21.5 million and $5.1 million were recorded as debt issuance costs and additional paid-in capital, respectively, in proportion to the allocation of the proceeds of the 2019 Convertible Notes. The $21.5 million of debt issuance costs recorded on the Company’s consolidated balance sheet are being amortized over the contractual term of the 2019 Convertible Notes using the effective-interest method.

During February 2014, the $1.15 billion aggregate principal amount of the 2019 Convertible Notes were initially allocated between long-term debt, or liability component, and additional paid-in capital, or equity component, within the Company’s consolidated balance sheet at $930.9 million and $219.1 million, respectively. The liability component was measured using the nonconvertible debt interest rate. The carrying amount of the equity component representing the conversion option was determined by deducting the fair value of the liability component from the face value of the 2019 Convertible Notes as a whole. Since the Company must still settle these 2019 Convertible Notes at face value at or prior to maturity, this liability component will be accreted up to its face value resulting in additional non-cash interest expense being recognized within the Company’s consolidated statements of income while the 2019 Convertible Notes remain outstanding. The effective-interest rate on the 2019 Convertible Notes is approximately 6.2% per annum. The equity component is not remeasured as long as it continues to meet the conditions for equity classification.

During March 2018, the Company issued $550 million aggregate principal amount of new convertible senior notes due 2024, or 2024 Convertible Notes as described below, and subsequently used the proceeds, along with cash on hand, to repurchase $475.0 million of its existing 2019 Convertible Notes from a limited number of holders in privately negotiated transactions for an aggregate purchase price of $583.5 million, which included $1.0 million of accrued interest. For accounting purposes, pursuant to ASC 470, Debt, these transactions were accounted for as an extinguishment of 2019 Convertible Notes and an issuance of new 2024 Convertible Notes. The Company allocated the purchase price between the fair value of the liability component and the equity component of the 2019 Convertible Notes at $459.4 million and $123.0 million, respectively. As a result, the Company recognized $446.4 million as a reduction to long-term debt representing the carrying value of the liability component and $123.0 million as a reduction to additional paid-in capital representing the equity component of the repurchased 2019 Convertible Notes. The $13.1 million difference between the fair value and carrying value of the liability component of the repurchased 2019 Convertible Notes was recognized as a loss on extinguishment of debt as a result of the transaction and is recorded in other expense (income), net within the Company’s consolidated statement of income. The accounting impact of the new 2024 Convertible Notes is described in further detail below.

As of December 31, 2018, the remaining outstanding principal on the 2019 Convertible Notes was $675.0 million, the unamortized debt discount and debt issuance costs were $18.6 million, and the carrying amount of the liability component was $656.4 million, which was recorded to Current portion of long-term debt within the Company’s consolidated balance sheet. As of December 31, 2017, the outstanding principal on the 2019 Convertible Notes was $1.15 billion, the unamortized debt discount and debt issuance costs were $80.0 million, and the carrying amount of the liability component was $1,070.0 million, which was recorded to Long-term debt within the Company’s consolidated balance sheet. The fair value of the liability component relating to the 2019 Convertible Notes was approximately $662.1 million and $1,066.0 million as of December 31, 2018 and 2017, respectively.

During the years ended December 31, 2018, 2017, and 2016, the Company recognized $48.5 million, $68.2 million, and $65.3 million, respectively, of interest expense relating to the 2019 Convertible Notes, which included $29.8 million, $41.2 million, and $38.6 million, respectively, relating to non-cash interest expense relating to the debt discount and $2.9 million, $4.0 million, and $3.8 million, respectively, relating to amortization of debt issuance costs.

In conjunction with the issuance of the 2019 Convertible Notes, during February 2014, the Company paid approximately $685.8 million to enter into prepaid forward share repurchase transactions, or the Forward Transactions, with certain financial institutions, and paid approximately $123.8 million to enter into capped call transactions with respect to its common shares, or the Capped Call Transactions, with certain financial institutions. Subsequently, in conjunction with the repurchase of a portion of the 2019 Convertible Notes, during March 2018, the Company entered into agreements with the option counterparties to the Capped Call Transactions to terminate a portion of such existing transactions. See Note 8, Shareholders’ Deficit, for additional discussion on the Forward Transactions and Capped Call Transactions entered into in conjunction with the issuance of these 2019 Convertible Notes.

Convertible Senior Notes due 2024

During March 2018, the Company issued $550 million aggregate principal amount of convertible senior notes, or the 2024 Convertible Notes, in a private offering to qualified institutional buyers, pursuant to Rule 144A under the Securities Act of 1933, as amended. The 2024 Convertible Notes are senior unsecured obligations which rank effectively subordinate to any of the Company’s existing and future secured indebtedness, including amounts outstanding under the 2018 Credit Facility, to the extent of the value of the assets securing such indebtedness. The 2024 Convertible Notes pay interest at a rate of 2.625% per annum payable semiannually in arrears on March 15 and September 15 of each year, beginning on September 15, 2018. The 2024 Convertible Notes mature on March 15, 2024, unless redeemed, repurchased or converted in accordance with their terms prior to such date. Holders of the 2024 Convertible Notes may convert their notes at their option under the following circumstances: (i) during any calendar quarter commencing after the calendar quarter ending June 30, 2018, if the last reported sale price of the Company’s common shares for at least 20 trading days (whether or not consecutive) in a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter exceeds 130% of the conversion price for the 2024 Convertible Notes on each applicable trading day; (ii) during the five business-day period immediately after any five consecutive trading day period, or the measurement period, in which the trading price per $1,000 principal amount of 2024 Convertible Notes for each trading day of that measurement period was less than 98% of the product of the last reported sale price of the Company’s common shares and the conversion rate for the 2024 Convertible Notes for each such day; (iii) if the Company calls the 2024 Convertible Notes for redemption; or (iv) upon the occurrence of specified corporate events. On and after December 15, 2023, holders may convert their 2024 Convertible Notes at any time, regardless of the foregoing circumstances. Upon conversion, the 2024 Convertible Notes will be settled, at the Company’s election, in cash, the Company’s common shares, or a combination thereof, based on the applicable conversion rate at such time. The 2024 Convertible Notes had an initial conversion rate of 16.0056 common shares per $1,000 principal amount of the 2024 Convertible Notes, or an initial conversion price of approximately $62.48 per common share, based on the retroactive adjustment due to the Company’s two-for-one stock split described in Note 2, Basis of Presentation. The conversion rate is subject to adjustment upon the occurrence of certain events and was 16.0352 common shares per $1,000 principal amount of the 2024 Convertible Notes, or a conversion price of approximately $62.36 per common share, as of December 31, 2018.

The Company incurred approximately $12.9 million of issuance costs during the first quarter of 2018 relating to the issuance of the 2024 Convertible Notes. Of the $12.9 million issuance costs incurred, $9.6 million and $3.3 million were recorded as debt issuance costs and additional paid-in capital, respectively, in proportion to the allocation of the proceeds of the 2024 Convertible Notes. The $9.6 million of debt issuance costs, which was recorded as an additional debt discount on the Company’s consolidated balance sheet, are being amortized over the contractual term of the 2024 Convertible Notes using the effective-interest method.

During March 2018, the $550 million aggregate principal amount of the 2024 Convertible Notes were initially allocated between long-term debt, or liability component, and additional paid-in-capital, or equity component, within the Company’s consolidated balance sheet at $410.1 million and $139.9 million, respectively. The liability component was measured using the nonconvertible debt interest rate. The carrying amount of the equity component representing the conversion option was determined by deducting the fair value of the liability component from the face value of the 2024 Convertible Notes as a whole. Since the Company must still settle these 2024 Convertible Notes at face value at or prior to maturity, this liability component will be accreted up to its face value resulting in additional non-cash interest expense being recognized within the Company’s consolidated statements of income while the 2024 Convertible Notes remain outstanding. The effective-interest rate on the 2024 Convertible Notes is approximately 8.4% per annum. The equity component is not remeasured as long as it continues to meet the conditions for equity classification.

As of December 31, 2018, the outstanding principal on the 2024 Convertible Notes was $550.0 million, the unamortized debt discount and debt issuance costs were $134.0 million, and the carrying amount of the liability component was $416.0 million, which was recorded to Long-term debt within the Company’s consolidated balance sheet. The fair value of the liability component relating to the 2024 Convertible Notes was approximately $448.1 million as of December 31, 2018.

During the year ended December 31, 2018, the Company recognized $26.6 million of interest expense relating to the 2024 Convertible Notes, which included $14.5 million relating to non-cash interest expense relating to the debt discount and $1.0 million relating to amortization of debt issuance costs.

Senior Notes due 2026

During August 2018, the Company issued $400 million aggregate principal amount of senior notes, or the 2026 Notes, in a private offering in the United States to qualified institutional buyers, pursuant to Rule 144A under the Securities Act of 1933, as amended, and outside the United States pursuant to Regulation S under the Securities Act of 1933, as amended. The 2026 Notes are senior unsecured obligations which rank effectively subordinate to any of the Company’s existing and future secured indebtedness, including amounts outstanding under the 2018 Credit Facility, to the extent of the value of the assets securing such indebtedness. The 2026 Notes pay interest at a rate of 7.250% per annum payable semiannually in arrears on February 15 and August 15 of each year, beginning on February 15, 2019. The 2026 Notes mature on August 15, 2026.

At any time prior to August 15, 2021, the Company may redeem all or part of the 2026 Notes at a redemption price equal to 100% of their principal amount, plus a “make whole” premium as of the redemption date, and accrued and unpaid interest to the redemption date. In addition, at any time prior to August 15, 2021, the Company may redeem up to 40% of the aggregate principal amount of the 2026 Notes with the proceeds of one or more equity offerings, at a redemption price equal to 107.250%, plus accrued and unpaid interest. Furthermore, at any time on or after August 15, 2021, the Company may redeem all or part of the 2026 Notes at the following redemption prices, expressed as percentages of principal amount, plus accrued and unpaid interest thereon to the redemption date, if redeemed during the twelve-month period beginning on August 15 of the years indicated below:

The 2026 Notes contain customary negative covenants, including, among other things, limitations or prohibitions on restricted payments, incurrence of additional indebtedness, liens, mergers, asset sales and transactions with affiliates. In addition, the 2026 Notes contain customary events of default.

The Company incurred approximately $5.4 million of issuance costs during the third quarter of 2018 relating to the issuance of the 2026 Notes. The $5.4 million of debt issuance costs, which was recorded as a debt discount on the Company’s consolidated balance sheet, are being amortized over the contractual term of the 2026 Notes using the effective-interest method.

As of December 31, 2018, the outstanding principal on the 2026 Notes was $400.0 million, the unamortized debt issuance costs were $5.2 million, and the carrying amount was $394.8 million, which was recorded to long-term debt within the Company’s consolidated balance sheet. The fair value of the 2026 Notes was approximately $394.6 million as of December 31, 2018 and was determined by utilizing over-the-counter market quotes and yield curves, which are considered Level 2 inputs as defined in Note 13, Fair Value Measurements.

During the year ended December 31, 2018, the Company recognized $11.1 million of interest expense relating to the 2026 Notes, which included $0.2 million relating to amortization of debt issuance costs.

Valuation of 2019 Convertible Notes and 2024 Convertible Notes – Level 2 and Level 3 Inputs

In order to determine the initial value of the 2019 Convertible Notes and the 2024 Convertible Notes, the Company determined the fair value of the liability component of the 2019 Convertible Notes and the 2024 Convertible Notes using two valuation methods. The Company reviewed market data that was available for publicly traded, senior, unsecured nonconvertible corporate bonds issued by companies with similar credit ratings. Assumptions used in the estimate represent what market participants would use in pricing the liability component, including market yields and credit standing to develop the straight debt yield estimate. The Company also used a lattice model, which included inputs such as stock price, the Convertible Note trading price, volatility and dividend yield to estimate the straight debt yield. The Company combined the results of the two valuation methods to determine the fair value of the liability component of the 2019 Convertible Notes and the 2024 Convertible Notes. Most of these inputs are primarily considered Level 2 and Level 3 inputs. The Company used similar valuation approaches to determine the subsequent fair value of the liability component only for disclosure purposes, which includes using a lattice model and (1) reviewing market data relating to its 2026 Notes and comparable yield curves to determine its straight debt yield estimate, or (2) reviewing market data relating to publicly traded, senior, unsecured nonconvertible corporate bonds issued by companies with similar credit ratings in order to determine its straight debt yield estimate.

Total Debt

The Company’s total interest expense was $181.0 million, $160.8 million, and $99.3 million, for the years ended December 31, 2018, 2017, and 2016, respectively, which was recognized within its consolidated statements of income.

As of December 31, 2018, annual scheduled principal payments of debt were as follows:

Certain vendors and government agencies may require letters of credit or similar guaranteeing arrangements to be issued or executed. As of December 31, 2018, the Company had $38.2 million of issued but undrawn letters of credit or similar arrangements, which included the Mexico Value Added Tax, or VAT, related surety bonds described in Note 7, Contingencies.