Debt (Schedule of Line of Credit Facilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019	Dec. 20, 2017
Line of Credit Facility [Line Items]
Line of credit facility, remaining borrowing capacity	$ 45,000	$ 45,000
Total debt	976,900	977,155
Debt instrument, unused borrowing capacity, amount	31,912	32,044
Letter of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	13,088	12,956
Debt instrument, unused borrowing capacity, amount	111,912	112,044
Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, remaining borrowing capacity	125,000	125,000	$ 125,000
Line of Credit | Letter of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	194	204
Revolving Credit Facility
Line of Credit Facility [Line Items]
Total debt	$ 0	$ 0