Interest expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Interest Expense [Abstract]
Interest expense on long-term debt and obligations under capital lease	$ 27,090	$ 27,380	$ 30,270
Withholding tax provision classified as interest	0	(1,476)	2,576
Interest on legal settlements	(979)	3,294	0
Amortization of debt issuance costs and discount on secured term loan	3,044	2,903	3,921
Total interest expense	$ 29,155	$ 32,101	$ 36,767