XML 92 R91.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2
Share-Based Compensation - Restricted Stock Units Narrative (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award      
Fair value of restricted stocks granted $ 18.9 $ 5.9 $ 59.4
Restricted Stock Units      
Share-based Compensation Arrangement by Share-based Payment Award      
Fair value of restricted stocks granted $ 59.7 $ 37.7 $ 36.9
Increase in estimated number of shares expected vest (in shares) 100,000    
Restricted stocks available for future grant under the Company's option plans (in shares) 200,000    
Restricted Stock Units | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award      
Vesting period of restricted stocks 3 years    
Restricted Stock Units | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award      
Vesting period of restricted stocks 4 years