Income taxes (Benefit (Provision) for Income Taxes) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Current:
Federal	$ 30	$ 58	$ (88)
State	(27)	(137)	(257)
Current Income Tax Expense (Benefit) Net	3	(79)	(345)
Deferred Federal Income Tax Expense (Benefit)	50,143	0	(10,027)
Provision (benefit) for income taxes	$ 50,146	$ (79)	$ (10,372)