Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Total Revenue	$ 65,182	$ 61,555	$ 61,506	$ 57,852	$ 50,691	$ 51,459	$ 54,798	$ 52,238	$ 246,094	$ 209,185
Prime Contractor
Disaggregation of Revenue [Line Items]
Total Revenue									215,241	193,448
Subcontractor
Disaggregation of Revenue [Line Items]
Total Revenue									30,853	15,737
Time and Materials
Disaggregation of Revenue [Line Items]
Total Revenue									185,656	147,509
Cost Reimbursable
Disaggregation of Revenue [Line Items]
Total Revenue									48,101	58,091
Firm Fixed Price
Disaggregation of Revenue [Line Items]
Total Revenue									$ 12,337	$ 3,585