Commitments and Contingencies (Schedule of Letters of Credit and Surety Bonds) (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Sep. 30, 2020
Other Commitments [Line Items]
Debt instrument, unused borrowing capacity, amount	$ 33,176	$ 32,037
Line of credit facility, remaining borrowing capacity	45,000	45,000
Surety Bond [Member]
Other Commitments [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	230,000	230,000
Guarantor Obligations, Current Carrying Value	144,647	152,990
Guarantor Obligations, Remaining Surety Bonds Available	$ 85,353	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	$ 11,824	12,963
Debt instrument, unused borrowing capacity, amount	$ 113,176	$ 112,037