Annual report pursuant to Section 13 and 15(d)

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

v3.10.0.1
Share-Based Compensation - Summary of Activities Under Share-Based Compensation Plans (Parenthetical) (Detail) - shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of Shares, Expected to vest 1,111,000  
Market condition awards [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Outstanding SARs   200,000
Exercised SARs 200,000  
Market condition awards [Member] | Maximum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Outstanding SARs 100,000  
Exercisable SARs 100,000  
Performance condition SARs [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Outstanding SARs 3,100,000 6,200,000
Exercised SARs 3,000,000  
Forfeited SARs 100,000  
Exercisable SARs 1,800,000  
Performance Based Stock Unit Awards [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of Shares, Expected to vest 261,297  
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 outstanding and nonvested that can vest maximum 708,836 268,776
Number of share based payment awards other than options that can vest maximum 440,060