Debt (Schedule of Line of Credit Facilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2021		Sep. 30, 2020
Line of Credit Facility [Line Items]
Line of credit facility, remaining borrowing capacity	$ 45,000		$ 45,000
Total debt	889,427		885,470
Debt instrument, unused borrowing capacity, amount	33,096		32,037
Letter of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	11,904		12,963
Debt instrument, unused borrowing capacity, amount	113,096		112,037
Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, remaining borrowing capacity	125,000		125,000
Line of Credit | Letter of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	33		52
Revolving Credit Facility
Line of Credit Facility [Line Items]
Total debt	$ 0	[1]	$ 0

[1] On April 1, 2021, the Company paid off the outstanding balance of the First Lien Term Loan (as defined below) and entered into the 2021 Credit Agreement (as defined below). See Note 23, “Subsequent Events” for further discussion.