Stock incentive plans (Details 6) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) item $ / shares shares
RSU
Number of Shares
Non-vested at beginning of period (in shares)	1,385,000
Granted (in shares)	1,472,000
Vested (in shares)	(949,000)
Canceled/ forfeited (in shares)	(89,000)
Non-vested at end of period (in shares)	1,819,000
Weighted Average Grant-Date Fair Value
Non-vested at beginning period (In dollars per share) | $ / shares	$ 6.09
Granted (In dollars per share) | $ / shares	7.55
Vested (In dollars per share) | $ / shares	7.69
Canceled/forfeited (In dollars per share) | $ / shares	7.14
Non-vested at end of period (In dollars per share) | $ / shares	$ 6.39
Total unrecognized stock-based compensation expense | $	$ 9,510
Weighted average period over which unrecognized compensation expense is expected to be recognized	1 year 11 months 12 days
Time-based restricted stock unit awards
Number of Shares
Vested (in shares)	(949,254)
Weighted Average Grant-Date Fair Value
Shares of common stock issued resulting from vesting	618,238
Time-based restricted stock unit awards | Executive and non executive personnel | Minimum
Stock incentive plans
Vesting period	2 years
Time-based restricted stock unit awards | Executive and non executive personnel | Maximum
Stock incentive plans
Vesting period	3 years
Time-based restricted stock unit awards | Existing board members
Stock incentive plans
Vesting period	1 year
Time-based restricted stock unit awards | New board members
Stock incentive plans
Vesting period	4 years
Vesting percentage when the individual completes 12 months of continuous service	25.00%
Performance-based restricted stock unit awards
Stock incentive plans
Vesting percentage when the individual completes 12 months of continuous service	33.00%
Continuous service period of individual	12 months
Number of equal quarterly installments for remaining award vesting | item	8