v3.19.1
Stock incentive plans - Restricted stock unit awards (Details) - $ / shares
1 Months Ended 3 Months Ended
Feb. 28, 2019
Mar. 31, 2019
Stock incentive plans    
Shares of common stock issued resulting from vesting   1,306,000
RSUs    
Number of Shares    
Non-vested at beginning of period (in shares)   3,119,000
Granted (in shares)   517,000
Vested (in shares)   (2,656,000)
Canceled/forfeited (in shares)   (10,000)
Non vested at end of period (in shares)   970,000
Weighted Average Grant Date Fair Value    
Non-vested at beginning of period (in dollars per share)   $ 8.60
Granted (in dollars per share)   23.36
Vested (in dollars per share)   6.58
Canceled/forfeited (in dollars per share)   25.51
Non vested at end of period (in dollars per share)   $ 21.80
Service-based restricted stock unit awards | Executive And Non Executive Member | Maximum    
Stock incentive plans    
Vesting period   3 years
Service-based restricted stock unit awards | Non-employee directors and existing members    
Stock incentive plans    
Vesting period   1 year
Service-based restricted stock unit awards | Non-employee directors and new members    
Stock incentive plans    
Vesting percentage when the individual completes 12 months of continuous service   33.30%
Vesting period   3 years
Performance-based restricted stock unit awards    
Stock incentive plans    
Vesting period   3 years
Number of Shares    
Granted (in shares) 29,000  
Weighted Average Grant Date Fair Value    
Granted (in dollars per share) $ 11.94  
Performance-based restricted stock unit awards | Minimum    
Stock incentive plans    
Performance objective threshold (as a percent)   50.00%
Performance-based restricted stock unit awards | Maximum    
Stock incentive plans    
Performance objective threshold (as a percent)   150.00%