Debt (Schedule of Line of Credit Facilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Sep. 30, 2019
Line of Credit Facility [Line Items]
Line of credit facility, remaining borrowing capacity	$ 45,000	$ 45,000
Total debt	879,927	977,155
Debt instrument, unused borrowing capacity, amount	33,128	32,044
Letter of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	11,872	12,956
Debt instrument, unused borrowing capacity, amount	113,128	112,044
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	51	204
Revolving Credit Facility
Line of Credit Facility [Line Items]
Total debt	$ 0	$ 0