Annual report pursuant to Section 13 and 15(d)

Share-Based Compensation - Summary of Activity Under Share-Based Compensation Plans (Parenthetical) (Detail)

v3.8.0.1
Share-Based Compensation - Summary of Activity Under Share-Based Compensation Plans (Parenthetical) (Detail) - shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Market condition awards [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Outstanding SARs 100,000 100,000
Performance condition SARs [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Outstanding SARs 3,100,000 2,900,000
Exercisable SARs 1,500,000  
Performance Based Stock Unit Awards [Member] | Maximum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of share based payment awards other than options that can vest maximum 134,388