Summary of Significant Accounting Policies - Accounts Receivable (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Customer receivables	$ 56,934	$ 59,263
Unbilled receivables	65,417	52,278
Other receivables	702	751
Rebates receivable	2,468	1,442
Allowance for doubtful accounts	(2,187)	(1,665)
Accounts receivable, net	$ 123,334	$ 112,069