Revenues (Narrative) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Government contract receivables	$ 10,000	$ 9,300
Accrued expenses for subcontractor fees	5,500	1,800
Prepaid Expenses and Other Current Assets
Disaggregation of Revenue [Line Items]
Unbilled contracts receivable	$ 0	$ 465