Contract Balances - Unbilled Receivables and Deferred Revenue (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Jan. 01, 2016
Accounts receivable, net:
Unbilled trade receivables, current	$ 10,192	$ 12,316
Prepaid expenses and other current assets:
Unbilled non-trade receivables, current	8,021	8,711
Other assets:
Unbilled trade receivables, non-current	6,076	7,684
Unbilled non-trade receivables, non-current	8,923	8,884
Deferred revenue, current	(89,246)	(85,790)
Deferred revenue, non-current	(349)	(484)
Total deferred revenue, net	$ (56,383)	$ (48,679)	$ (54,200)