Income taxes - Schedule of Current and Deferred Income Tax (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current:
U.S. federal tax (benefit)	$ (1,738)	$ 10,302	$ (2,984)
State and local tax	832	1,520	1,885
Non-U.S. operations	181	(264)	116
Total Current	(725)	11,558	(983)
Deferred:
U.S. federal tax	3,173	1,273	16,658
State and local tax	1,145	2,057	2,482
Non-U.S. operations	220	1,287	(401)
Deferred income taxes	4,538	4,617	18,739
Total	$ 3,813	$ 16,175	$ 17,756