Annual report pursuant to Section 13 and 15(d)

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

v3.20.4
Share-Based Compensation - Summary of Activities Under Share-Based Compensation Plans (Parenthetical) (Detail) - shares
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of Shares, Expected to vest [1] 2,846,000  
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 1,100,000 2,900,000
Exercised SARs 1,800,000  
Exercisable SARs 1,100,000  
Performance Based Stock Unit Awards [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of shares, granted during period 504,908  
Number of Shares, Expected to vest 228,996  
Number of Shares, Forfeited 38,746  
Number of Shares, Vested 561,280  
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 712,596 475,430
[1] Includes 561,280 performance-based stock unit awards.