Debt (Shelf Facility Agreements) (Narrative) (Details)	1 Months Ended	9 Months Ended
	Jun. 30, 2021 USD ($)	May 29, 2021 USD ($)	Aug. 29, 2020 USD ($)
Line of Credit Facility [Line Items]
Maximum consolidated leverage ratio of total indebtedness to EBITDA		3.00
Maximum consolidated leverage ratio of total indebtedness to EBITDA after material acquisition		3.50
Minimum consolidated interest coverage ratio of EBITDA to total interest expense		3.00
Met Life Note Purchase Agreement [Member]
Line of Credit Facility [Line Items]
Credit facility, maximum borrowing capacity		$ 250,000,000
Remaining borrowing capacity		180,000,000
Prudential Note Purchase Agreement [Member]
Line of Credit Facility [Line Items]
Credit facility, maximum borrowing capacity		250,000,000
Remaining borrowing capacity		200,000,000
Series 2018B notes, due June 11, 2021 [Member] | Private Placement Debt [Member]
Line of Credit Facility [Line Items]
Principal amount		$ 20,000,000	$ 20,000,000
Interest rate		3.42%	3.42%
Maturity date		Jun. 11, 2021
Series 2018B notes, due June 11, 2021 [Member] | Subsequent Event [Member] | Private Placement Debt [Member]
Line of Credit Facility [Line Items]
Repayment of debt	$ 20,000,000