Commitments and Contingencies (Schedule of Letters of Credit and Surety Bonds) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Other Commitments [Line Items]
Line of credit facility, remaining borrowing capacity	$ 45,000	$ 45,000
Debt instrument, unused borrowing capacity, amount	32,037	32,044
Surety Bond [Member]
Other Commitments [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	230,000	220,000
Guarantor Obligations, Current Carrying Value	152,990	144,717
Guarantor Obligations, Remaining Surety Bonds Available	$ 77,010	$ 75,283
Minimum [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Letter of Credit, Guarantee, Bond Commitments, Expiration Period	12 months
Maximum [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Letter of Credit, Guarantee, Bond Commitments, Expiration Period	10 years