Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Total revenue	$ 50,691	$ 51,459	$ 54,798	$ 52,238	$ 54,183	$ 38,700	$ 33,756	$ 33,752	$ 209,185	$ 160,391
Prime contractor
Disaggregation of Revenue [Line Items]
Total revenue									193,448	154,207
Subcontractor
Disaggregation of Revenue [Line Items]
Total revenue									15,737	6,184
Time and materials
Disaggregation of Revenue [Line Items]
Total revenue									147,509	134,136
Cost reimbursable
Disaggregation of Revenue [Line Items]
Total revenue									58,091	23,200
Firm fixed price
Disaggregation of Revenue [Line Items]
Total revenue									3,585	3,055
Department of Veterans Affairs
Disaggregation of Revenue [Line Items]
Total revenue									100,204	91,949
Department of Health and Human Services
Disaggregation of Revenue [Line Items]
Total revenue									95,026	62,000
Other
Disaggregation of Revenue [Line Items]
Total revenue									$ 13,955	$ 6,442