Commitments and Contingencies (Schedule of Letters of Credit and Surety Bonds) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Sep. 30, 2020
Other Commitments [Line Items]
Debt instrument, unused borrowing capacity, amount	$ 33,096	$ 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	250,000	230,000
Guarantor Obligations, Current Carrying Value	147,565	152,990
Guarantor Obligations, Remaining Surety Bonds Available	$ 102,435	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	$ 11,904	12,963
Debt instrument, unused borrowing capacity, amount	$ 113,096	$ 112,037