| Long-Term Debt - Schedule of Long-Term Debt (Parenthetical) (Detail) | 1 Months Ended | 3 Months Ended | |
|---|---|---|---|
| Mar. 31, 2018 | Feb. 28, 2014 | Mar. 31, 2018 | |
| 2.000% Convertible Senior Notes Due 2019 [Member] | |||
| Debt Instrument [Line Items] | |||
| Convertible notes, interest rate | 2.00% | 2.00% | 2.00% | 
| Convertible notes maturity | Aug. 15, 2019 | Aug. 15, 2019 | |
| 2.625% Convertible Senior Notes Due 2024 [Member] | |||
| Debt Instrument [Line Items] | |||
| Convertible notes, interest rate | 2.625% | 2.625% | |
| Convertible notes maturity | Mar. 15, 2024 | Mar. 15, 2024 | |
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- Definition Contractual interest rate for funds borrowed, under the debt agreement. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
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- Definition Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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