Commitments and Contingencies (Schedule of Letters of Credit and Surety Bonds) (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2021	Sep. 30, 2020
Other Commitments [Line Items]
Debt instrument, unused borrowing capacity, amount	$ 48,496	$ 32,037
Line of credit facility, remaining borrowing capacity	60,000	45,000
Other Current Liabilities
Other Commitments [Line Items]
Loss Contingency Accrual	16,650
Other Current Assets
Other Commitments [Line Items]
Loss Contingency, Receivable	16,650
Surety Bond [Member]
Other Commitments [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	250,000	230,000
Guarantor Obligations, Current Carrying Value	141,837	152,990
Guarantor Obligations, Remaining Surety Bonds Available	$ 108,163	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
Letter of Credit
Other Commitments [Line Items]
Letters of credit outstanding, amount	$ 11,504	12,963
Debt instrument, unused borrowing capacity, amount	$ 243,496	$ 112,037