Revenue Recognition - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Fire & Emergency
Disaggregation Of Revenue [Line Items]
Interest Expense, Customer Deposits	$ 15.6	$ 14.5	$ 18.1
Customer Concentration Risk \| Sales Revenue, Net \| Defense \| DoD
Disaggregation Of Revenue [Line Items]
Concentration Risk, Percentage	98.00%	97.00%	90.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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