Summary of Significant Accounting Policies - Accounts Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Customer receivables	$ 52,567	$ 59,263
Unbilled receivables	58,445	52,278
Other receivables	816	751
Rebates receivable	1,638	1,442
Allowance for doubtful accounts	(2,454)	(1,665)
Accounts receivable, net	$ 111,012	$ 112,069