Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Total revenue	$ 54,183	$ 38,700	$ 33,756	$ 33,752	$ 32,489	$ 36,131	$ 34,401	$ 30,215	$ 160,391	$ 133,236
Prime
Disaggregation of Revenue [Line Items]
Total revenue									154,207
Subcontractor
Disaggregation of Revenue [Line Items]
Total revenue									6,184
Time and materials
Disaggregation of Revenue [Line Items]
Total revenue									134,136
Cost reimbursable
Disaggregation of Revenue [Line Items]
Total revenue									23,200
Firm fixed price
Disaggregation of Revenue [Line Items]
Total revenue									3,055
Department of Veterans Affairs
Disaggregation of Revenue [Line Items]
Total revenue									91,949
Department of Health and Human Services
Disaggregation of Revenue [Line Items]
Total revenue									62,000
Other
Disaggregation of Revenue [Line Items]
Total revenue									$ 6,442