Stock incentive plans (Details 6) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2014 item	Dec. 31, 2013 item
Weighted Average Grant-Date Fair Value
Shares issued	176,835
RSU
Number of Shares
Nonvested at the beginning of the period (in shares)	753,000
Granted (in shares)	1,343,000
Vested (in shares)	(279,000)
Forfeited (in shares)	(8,000)
Nonvested at the end of the period (in shares)	1,809,000
Weighted Average Grant-Date Fair Value
Nonvested at the beginning of the period (In dollars per share)	$ 6.22
Granted (In dollars per share)	$ 5.88
Vested (In dollars per share)	$ 6.05
Canceled/forfeited (In dollars per share)	$ 6.05
Nonvested at the end of the period (In dollars per share)	$ 5.99
Time-based restricted stock unit awards
Weighted Average Grant-Date Fair Value
Shares vested	278,545
Time-based restricted stock unit awards | Executive and non executive
Stock incentive plans
Vesting period		2 years
Vesting percentage when the individual completes 12 months of continuous service		50.00%
Continuous service period of individual		12 months
Number of equal quarterly installments for award vesting	12
Number of equal quarterly installments for remaining award vesting		4
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