Debt (Schedule of Line of Credit Facilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Line of Credit Facility [Line Items]
Line of credit facility, remaining borrowing capacity	$ 45,000	$ 45,000
Total debt	885,470	977,155
Debt instrument, unused borrowing capacity, amount	32,037	32,044
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	12,963	12,956
Debt instrument, unused borrowing capacity, amount	112,037	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 [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	52	204
Revolving Credit Facility
Line of Credit Facility [Line Items]
Total debt	$ 0	$ 0