v3.6.0.2
Subsequent events (Details) - shares
1 Months Ended 12 Months Ended
Feb. 28, 2017
Dec. 31, 2016
Performance-based restricted stock unit awards    
Subsequent events    
Vesting period   3 years
Subsequent Event | Executive members | Time-based restricted stock unit awards    
Subsequent events    
Granted (in shares) 88,000  
Vesting period 3 years  
Subsequent Event | Executive members | Performance-based restricted stock unit awards    
Subsequent events    
Granted (in shares) 88,000  
Subsequent Event | Executive members | Performance-based restricted stock unit awards | Vesting not to exceed March 15, 2019    
Subsequent events    
Vesting percentage 66.67%  
Subsequent Event | Executive members | Performance-based restricted stock unit awards | Vesting on May 1, 2019    
Subsequent events    
Vesting percentage 8.33%  
Subsequent Event | Executive members | Performance-based restricted stock unit awards | Vesting quarterly after May 1, 2019    
Subsequent events    
Vesting percentage upon completion of continuous service 8.33%  
Subsequent Event | Non-executive personnel | Time-based restricted stock unit awards    
Subsequent events    
Granted (in shares) 304,000  
Vesting period 3 years