Interest expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest Expense [Abstract]
Interest expense on long-term debt and obligations under capital lease	$ 34,346	$ 29,425	$ 27,090
Interest on legal settlements	525	(28)	(979)
Amortization of debt issuance costs and discount on secured term loan	3,003	3,682	3,044
Interest capitalized	(4,832)	(624)	0
Total interest expense	$ 33,042	$ 32,455	$ 29,155