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Employee Stock Purchase Plan, Stock Options and Warrants - Narrative (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation cost not yet recognized $ 19.0    
Compensation cost not yet recognized, period of recognition 3 years 1 month 2 days    
Options granted in period (in shares) 692,000 1,300,000 880,000
Fair value of options, net of forfeitures $ 11.1 $ 12.4 $ 5.2
Options granted in period, weighted average grant date fair value (in dollars per share) $ 16.05 $ 9.57 $ 5.94
2006 Incentive Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares available for grant (in shares) 2,900,000    
2006 Incentive Plan | Stock Options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Option contractual life 7 years    
2006 Incentive Plan | Stock Options | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 3 years    
2006 Incentive Plan | Stock Options | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 5 years    
Employee Stock Purchase Plan Qualified      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares available for grant (in shares) 105,207    
Purchase price for ESPP, percent of market price 95.00%