Other Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Other Liabilities
Interest rate swap contracts, Current	$ 407	$ 7,314
Asset retirement obligations	6,954	9,837
Deferred revenue, current	2,966	3,590
Other, Current	9,363	10,629
Total current portion of other long-term liabilities	19,690	31,370
Acquisition-related contingent consideration	38,369	42,614
Interest rate swap contracts, Noncurrent		3,547
Deferred revenue, noncurrent	2,905	2,063
Other, Noncurrent	18,470	26,778
Total other long-term liabilities	$ 59,744	$ 75,002