Commitments and Contingencies (Schedule of Letters of Credit and Surety Bonds) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Mar. 31, 2022	Mar. 31, 2022	Sep. 30, 2021
Other Commitments [Line Items]
Revolving credit capacity	$ 60,000	$ 60,000	$ 60,000
Remaining revolving credit capacity	50,396	50,396	49,888
Surety Bond
Other Commitments [Line Items]
Surety capacity	252,225	252,225	250,000
Surety issuances	122,086	122,086	147,845
Remaining surety available	$ 130,139	130,139	102,155
Minimum | Surety Bond
Other Commitments [Line Items]
Letter of Credit, Guarantee, Bond Commitments, Expiration Period	12 months
Maximum | Surety Bond
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	$ 9,604	9,604	10,112
Remaining revolving credit capacity	$ 119,396	$ 119,396	$ 302,888
Debt Instrument, Maturity Date		Mar. 20, 2030