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Stock-Based Compensation (Details)
$ / shares in Units, $ in Millions
3 Months Ended
Mar. 31, 2019
USD ($)
employee_stock_plan
$ / shares
shares
Mar. 31, 2018
USD ($)
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of active employee stock plans | employee_stock_plan 1  
Number of shares available for grant (in shares) 4,300,000  
Stock-based compensation expense (in USD) | $ $ 4.1 $ 8.0
Stock-based compensation amortization expense unrecognized (in USD) | $ $ 25.4  
Average remaining vesting period (in years) 2 years 4 months 13 days  
Restricted Stock    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of shares granted during the period (in shares) 0 1,100,000
Award vesting period (in years) 3 years  
Average grant date fair value (usd per share) | $ / shares   $ 11.81
Award vesting rights as a percentage 33.33%  
Restricted Stock Units    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of shares granted during the period (in shares) 532,000 450,000
Award vesting period (in years) 3 years  
Average grant date fair value (usd per share) | $ / shares $ 10.43 $ 12.35