Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation (Options) (Details)

v3.8.0.1
Stock-Based Compensation (Options) (Details) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Stock-Based compensation      
Cash received from exercises of stock options $ 2,404 $ 1,900  
Cash received from issuance of restricted stock $ 2 $ 3  
Weighted-Average Remaining Contractual Life      
Outstanding 4 years 1 month 6 days    
Stock options      
Options      
Outstanding at the beginning of the period (in shares) 2,254,565    
Exercised (in shares) (162,857)    
Forfeited (in shares) (1,668)    
Outstanding at the end of the period (in shares) 2,090,040   2,254,565
Options exercisable (in shares) 1,967,299    
Weighted-Average Exercise Price      
Outstanding at the beginning of the period (in dollars per share) $ 19.23    
Exercised (in dollars per share) 14.76    
Forfeited (in dollars per share) 32.46    
Outstanding at the end of the period (in dollars per share) 19.57   $ 19.23
Options exercisable (in dollars per share) $ 19.02    
Weighted-Average Remaining Contractual Life      
Outstanding     4 years 3 months 18 days
Options exercisable 3 years 9 months 18 days    
Aggregate Intrinsic Value      
Outstanding (in dollars) $ 78,859   $ 69,939
Options exercisable (in dollars) 75,310    
Additional disclosures      
Unrecognized stock-based compensation expense related to unvested stock options $ 1,458    
Unrecognized compensation expense weighted-average recognition period 1 year 7 months 6 days    
Stock options | Minimum      
Additional disclosures      
Exercise prices of stock options outstanding (in dollars per share) $ 7.15    
Stock options | Maximum      
Additional disclosures      
Exercise prices of stock options outstanding (in dollars per share) $ 55.29