Accounts Receivable - Summary of components of accounts receivable (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Trade receivables:
Billed	$ 122,216	$ 190,567
Unbilled	39,223	40,731
Other receivables	10,280	11,494
Total	171,719	242,792
Less: allowance for doubtful accounts	(2,553)	(10,605)
Accounts receivable, net	$ 169,166	$ 232,187