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Share-Based Compensation - Restricted Stock Units (Details) - Restricted Stock Units
$ / shares in Units, $ in Millions
6 Months Ended
Jun. 30, 2021
USD ($)
$ / shares
shares
RSU Activity  
Outstanding at the beginning of the period (in shares) | shares 750,821
Granted (in shares) | shares 297,138
Vested (in shares) | shares (71,826)
Forfeited (in shares) | shares (5,362)
Outstanding at the end of the period (in shares) | shares 970,771
Weighted-Average Grant-Date Fair Value  
Outstanding at the beginning of the period (in dollars per share) | $ / shares $ 60.88
Granted (in dollars per share) | $ / shares 81.20
Vested (in dollars per share) | $ / shares 60.39
Forfeited (in dollars per share) | $ / shares 62.15
Outstanding at the end of the period (in dollars per share) | $ / shares $ 67.22
Additional disclosures  
Total unrecognized compensation cost related to nonvested restricted stock and RSUs granted | $ $ 39.0
Weighted-average period over which unrecognized compensation cost is expected to be recognized 2 years 3 months 18 days
Total fair value of shares vested during the period | $ $ 4.3
Minimum  
Share-Based Compensation  
Vesting period 2 years
Maximum  
Share-Based Compensation  
Vesting period 4 years
Tranche One  
Share-Based Compensation  
Performance period 3 years
Tranche Two | Minimum  
Share-Based Compensation  
Performance period 1 year
Tranche Two | Maximum  
Share-Based Compensation  
Performance period 2 years