Income taxes (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current:
Federal	$ (58)	$ 88	$ 216
State	137	257	330
Current Income Tax Expense (Benefit) Net	79	345	546
Deferred	(597)	10,027	(10,027)
Provision (benefit) for income taxes	$ 79	$ 10,372	$ (9,481)