Business Overview (Details)	6 Months Ended
	Mar. 31, 2020 employee market business_area location	Mar. 31, 2019
Concentration Risk [Line Items]
Number of market focus areas | business_area	3
Number of market leveraging core competencies | market	7
Revenue from Contract with Customer | Customer concentration | HHS
Concentration Risk [Line Items]
Concentration risk percentage	47.00%	31.00%
Revenue from Contract with Customer | Customer concentration | VA
Concentration Risk [Line Items]
Concentration risk percentage	46.00%	67.00%
U.S.
Concentration Risk [Line Items]
Number of employees | employee	1,950
Number of locations in which entity operates	30
Overseas
Concentration Risk [Line Items]
Number of locations in which entity operates	1