Quarterly report pursuant to Section 13 or 15(d)

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

v3.19.1
Share-Based Compensation - Summary of Activity Under Share-Based Compensation Plans (Parenthetical) (Detail) - shares
3 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of Shares, Forfeited 403,000  
Number of Shares, Expected to vest 1,662,000  
Market condition awards [Member] | Maximum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Outstanding SARs 100,000 100,000
Exercisable SARs 100,000  
Performance condition SARs [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Outstanding SARs 2,900,000 3,100,000
Forfeited SARs 200,000  
Exercisable SARs 1,900,000  
Performance condition SARs [Member] | Maximum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Exercised SARs 100,000  
Performance Based Stock Unit Awards [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of Shares, Forfeited 357,032  
Number of Shares, Expected to vest 355,437  
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 556,504 708,836
Number of share based payment awards other than options that can vest maximum 204,700