Debt (Shelf Facility Agreements) (Narrative) (Details)	3 Months Ended
	Nov. 30, 2019 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
Series 2018A Notes [Member]
Line of Credit Facility [Line Items]
Principal amount	$ 20,000,000
Interest rate	3.22%
Maturity date	Jun. 11, 2020
Series 2018B Notes [Member]
Line of Credit Facility [Line Items]
Principal amount	$ 20,000,000
Interest rate	3.42%
Maturity date	Jun. 11, 2021
Senior Notes Due January 2023 [Member]
Line of Credit Facility [Line Items]
Principal amount	$ 50,000,000
Interest rate	3.04%
Maturity date	Jan. 12, 2023
Met Life Note Purchase Agreement [Member]
Line of Credit Facility [Line Items]
Credit facility, maximum borrowing capacity	$ 250,000,000
Remaining borrowing capacity	210,000,000
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