Commitments and Contingencies (Schedule of Letters of Credit and Surety Bonds) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Other Commitments [Line Items]
Line of credit facility, remaining borrowing capacity	$ 60,000	$ 45,000
Debt instrument, unused borrowing capacity, amount	49,888	32,037
Surety Bond [Member]
Other Commitments [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	250,000	230,000
Guarantor Obligations, Current Carrying Value	147,845	152,990
Guarantor Obligations, Remaining Surety Bonds Available	$ 102,155	$ 77,010
Minimum | Surety Bond [Member]
Other Commitments [Line Items]
Letter of Credit, Guarantee, Bond Commitments, Expiration Period	12 months
Maximum | Surety Bond [Member]
Other Commitments [Line Items]
Letter of Credit, Guarantee, Bond Commitments, Expiration Period	10 years