Credit Facilities, Short-term Borrowings and Long-term Debt (Schedule of Long-term Debt) (Details) - USD ($) $ in Thousands	6 Months Ended
Mar. 31, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Unamortized debt issuance costs	$ (2,299)	$ (2,478)
Long-term debt	970,866	864,899
Less: Current portion of long-term debt	101,643
Long-term debt, less current portion	$ 869,223	864,899
Series G Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Interest rate	3.42%
Maturity date	Nov. 15, 2020
Long-term debt	$ 50,000	50,000
Series H Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Interest rate	4.03%
Maturity date	Nov. 15, 2023
Long-term debt	$ 25,000	25,000
Series I Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Interest rate	4.18%
Maturity date	Nov. 15, 2025
Long-term debt	$ 25,000	25,000
Series J Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Variable interest rate	2.94%
Maturity date	Nov. 15, 2020
Long-term debt	$ 50,000	50,000
Series J Notes [Member] \| Notes Payable to Banks [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	1.25%
Series K Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Interest rate	4.03%
Maturity date	Nov. 15, 2023
Long-term debt	$ 50,000	50,000
Series L Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Variable interest rate	4.18%
Maturity date	Nov. 15, 2025
Long-term debt	$ 50,000	50,000
Series M Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Interest rate	1.12%
Maturity date	Sep. 23, 2026
Long-term debt	$ 44,162	43,770
Series N Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Interest rate	1.31%
Maturity date	Sep. 23, 2028
Long-term debt	$ 85,011	84,257
Series O Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Interest rate	1.57%
Maturity date	Sep. 23, 2031
Long-term debt	$ 47,474	47,053
Series P Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Interest rate	4.27%
Maturity date	May 30, 2025
Long-term debt	$ 85,000	85,000
Series Q Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Interest rate	4.35%
Maturity date	May 30, 2027
Long-term debt	$ 85,000	85,000
Series R Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Interest rate	4.41%
Maturity date	May 30, 2029
Long-term debt	$ 75,000	75,000
Series S Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Interest rate	4.46%
Maturity date	May 30, 2030
Long-term debt	$ 75,000	75,000
Series T Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Interest rate	4.61%
Maturity date	May 30, 2033
Long-term debt	$ 80,000	80,000
Finance Leases [Member]
Debt Instrument [Line Items]
Long-term debt	$ 3,617
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maturity date	Jun. 19, 2024
Long-term debt	$ 142,901	$ 42,297
Revolving Credit Facility [Member] \| Minimum [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	0.875%
Revolving Credit Facility [Member] \| Maximum [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	1.75%

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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