Interest expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Interest Expense [Abstract]
Interest expense on long-term debt and obligations under capital lease	$ 6,682	$ 7,565	$ 13,652	$ 15,617
Withholding tax provision classified as interest	(1,000)	0	(1,000)	0
Amortization of deferred financing costs and discount on secured term loan	798	956	1,443	2,439
Total interest expense	$ 6,480	$ 8,521	$ 14,095	$ 18,056