Quarterly report pursuant to Section 13 or 15(d)

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

v3.10.0.1
Share-Based Compensation - Summary of Activity Under Share-Based Compensation Plans (Parenthetical) (Detail) - shares
 6 Months Ended
Jun. 30, 2018
Dec. 31, 2017
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]    
Exercised SARs 1,700,000  
Forfeited SARs 100,000  
Exercisable SARs 3,200,000  
Performance condition SARs [Member] | Maximum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Outstanding SARs 4,500,000 6,200,000
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 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