Income taxes (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current Income Tax Expense (Benefit) [Abstract]
Federal	$ 0	$ 0	$ 0
State and local	(35)	53	(107)
Foreign	(94)	(160)	(252)
Total current income tax (expense)/benefit	(129)	(107)	(359)
Deferred Income Tax Expense (Benefit) [Abstract]
Federal	2,596	20	(1,061)
State and local	742	3	(182)
Total deferred income tax (expense)	3,338	23	(1,243)
Income tax provision	3,209	(84)	(1,602)
Non-recurring tax benefit	$ 4,500