Income taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Income taxes
Income tax expense (benefit)	$ 148	$ (467)
Effective tax rate (as a percent)	2.90%	32.10%
Deferred tax liabilities	2,177
Uncertain tax positions	450		445
Uncertain tax positions, reduction to deferred tax assets	106		106
Accrued interest, net of federal income tax benefits, and penalties	58		53
Unrecognized tax benefits that would affect the effective tax rate	$ 286