Revenue and Customers - Receivables, Contract Assets, and Contract Liabilities with Customers (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Current contract assets	$ 28,207	$ 21,229
Noncurrent contract assets	31,551	34,520
Total contract assets	59,758	55,749	$ 55,749
Current contract liabilities (deferred revenue)	(38,074)	(35,422)
Noncurrent contract liabilities (deferred revenue)	(60,602)	(73,439)
Total contract liabilities	$ (98,676)	$ (108,861)	$ (108,861)