v3.20.4
Stock incentive plans - Stock option awards (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Aggregate Intrinsic Value          
Cash proceeds from exercise of stock option     $ 708 $ 470 $ 9,979
Stock options          
Number of Options          
Outstanding at beginning of period (in shares)     235,000    
Exercised (in shares)     (105,000) (69,000) (972,000)
Canceled/forfeited (in shares)     (21,000)    
Outstanding and exercisable at end of period (in shares) 109,000 235,000 109,000 235,000  
Weighted Average Exercise Price          
Outstanding at beginning of period (in dollars per share)     $ 7.67    
Exercised (in dollars per share)     6.71    
Canceled/forfeited (in dollars per share)     12.15    
Outstanding and exercisable at end of period (in dollars per share) $ 7.75 $ 7.67 $ 7.75 $ 7.67  
Weighted-Average Remaining Contract Life (years)          
Outstanding and exercisable at end of period 1 year 9 months 18 days 2 years 7 months 6 days      
Aggregate Intrinsic Value          
Outstanding and exercisable at end of period $ 559 $ 870 $ 559 $ 870  
Total intrinsic value of stock options exercised (in dollars)     $ 697 $ 423 $ 14,935