Other Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Other Liabilities
Interest rate swap contracts, Current	$ 2,596	$ 7,314
Asset retirement obligations	6,342	9,837
Deferred revenue, current	3,667	3,590
Other, Current	10,272	10,629
Total current portion of other long-term liabilities	22,877	31,370
Acquisition-related contingent consideration	45,505	42,614
Interest rate swap contracts, Noncurrent		3,547
Deferred revenue, noncurrent	1,961	2,063
Other, Noncurrent	23,455	26,778
Total other long-term liabilities	$ 70,921	$ 75,002