v3.5.0.2
Stock incentive plans - Activities of Options (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 6 Months Ended 12 Months Ended
Jun. 30, 2016
Dec. 31, 2015
Number of Options    
Outstanding at the beginning of the period (in shares) 3,748  
Exercised (in shares) (333)  
Canceled/forfeited (in shares) (50)  
Outstanding at the end of the period (in shares) 3,365 3,748
Vested, exercisable and expected to vest at the end of the period (in shares) 3,353  
Exercisable at the end of the period (in shares) 3,134  
Weighted Average Exercise Price    
Outstanding at the beginning of the period (in dollars per share) $ 6.89  
Exercised (in dollars per share) 5.36  
Canceled/forfeited (in dollars per share) 7.52  
Outstanding at the end of the period (in dollars per share) 7.03 $ 6.89
Vested, exercisable and expected to vest at the end of the period (in dollars per share) 7.03  
Exercisable at the end of the period (in dollars per share) $ 7.08  
Weighted-Average Remaining Contract Life (years)    
Outstanding 4 years 4 months 24 days 5 years
Vested, exercisable and expected to vest at the end of the period 4 years 4 months 24 days  
Exercisable at the end of the period 4 years 2 months 12 days  
Aggregate Intrinsic Value    
Outstanding at the end of the period $ 10,909 $ 6,611
Vested, exercisable and expected to vest at the end of the period 10,888  
Exercisable at the end of the period $ 10,311