Business Overview - Revenues by Customer (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
Concentration Risk [Line Items]
Revenue	$ 65,182	$ 61,555	$ 61,506	$ 57,852	$ 50,691	$ 51,459	$ 54,798	$ 52,238	$ 246,094	$ 209,185
Revenue Concentration | Customer Concentration
Concentration Risk [Line Items]
Revenue									$ 246,094	$ 209,185
Percent of total revenue									100.00%	100.00%
Revenue Concentration | Customer Concentration | Department of Veterans Affairs
Concentration Risk [Line Items]
Revenue									$ 110,078	$ 100,204
Percent of total revenue									45.00%	48.00%
Revenue Concentration | Customer Concentration | Department of Health and Human Services
Concentration Risk [Line Items]
Revenue									$ 91,543	$ 95,026
Percent of total revenue									37.00%	45.00%
Revenue Concentration | Customer Concentration | Department of Defense
Concentration Risk [Line Items]
Revenue									$ 30,930	$ 1,303
Percent of total revenue									13.00%	1.00%
Revenue Concentration | Customer Concentration | Customers with less than 10% share of total revenue
Concentration Risk [Line Items]
Revenue									$ 13,543	$ 12,652
Percent of total revenue									5.00%	6.00%