v3.19.2
Stock incentive plans - Restricted stock unit awards (Details) - $ / shares
1 Months Ended 6 Months Ended
Feb. 28, 2019
Jun. 30, 2019
Stock incentive plans    
Shares of common stock issued resulting from vesting   1,423,000
RSUs    
Number of Shares    
Non-vested at beginning of period (in shares)   3,119,000
Granted (in shares)   593,000
Vested (in shares)   (2,806,000)
Canceled/forfeited (in shares)   (51,000)
Non-vested at end of period (in shares)   855,000
Weighted Average Grant Date Fair Value    
Non-vested at beginning of period (in dollars per share)   $ 8.60
Granted (in dollars per share)   22.76
Vested (in dollars per share)   7.21
Canceled/forfeited (in dollars per share)   23.31
Non-vested at end of period (in dollars per share)   $ 22.08
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%