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Debt (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
Debt (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Debt Instrument [Line Items]
Available to borrow under the credit facility	$ 204,000
Cash on hand	30,477	$ 45,516	$ 53,825	$ 39,411
Letters of Credit Outstanding, Amount	7,800	9,700
Maximum aggregate short-term borrowings at any month-end	271,000	298,000
Average aggregate short-term borrowings outstanding	$ 258,800	$ 211,300
Weighted average interest rates	3.03%	2.09%	1.58%
Long-term Debt, Current Maturities	$ 20,000	$ 20,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Amount Outstanding	450,000
Line of Credit Facility, Commitment Fee Amount	$ 250,000
Minimum [Member]
Debt Instrument [Line Items]
Credit facility fees	12.50%
Maximum [Member]
Debt Instrument [Line Items]
Incremental term loan	$ 250,000
Credit facility fees	27.50%