Credit Facilities, Short-term Borrowings and Long-term Debt (Schedule of Long-term Debt) (Details) - USD ($) $ in Thousands	9 Months Ended
Jun. 30, 2019	Sep. 30, 2018
Debt Instrument [Line Items]
Long-term debt	$ 1,011,147	$ 1,092,397
Unamortized debt issuance costs	(2,589)	(2,895)
Less: Current portion of long-term debt
Long-term debt, less current portion	$ 1,011,147	1,092,397
Series D Notes [Member]
Debt Instrument [Line Items]
Interest rate	6.39%
Maturity date	Oct. 01, 2018
Series D Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt		100,000
Series F Notes [Member]
Debt Instrument [Line Items]
Interest rate	8.24%
Maturity date	Apr. 03, 2019
Series F Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt		43,000
Series G Notes [Member]
Debt Instrument [Line Items]
Interest rate	3.42%
Maturity date	Nov. 15, 2020
Series G Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 50,000	50,000
Series H Notes [Member]
Debt Instrument [Line Items]
Interest rate	4.03%
Maturity date	Nov. 15, 2023
Series H Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 25,000	25,000
Series I Notes [Member]
Debt Instrument [Line Items]
Interest rate	4.18%
Maturity date	Nov. 15, 2025
Series I Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 25,000	25,000
Series J Notes [Member]
Debt Instrument [Line Items]
Variable interest rate	3.77%
Maturity date	Nov. 15, 2020
Series J Notes [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Variable interest rate	1.25%
Series J Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 50,000	50,000
Series K Notes [Member]
Debt Instrument [Line Items]
Interest rate	4.03%
Maturity date	Nov. 15, 2023
Series K Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 50,000	50,000
Series L Notes [Member]
Debt Instrument [Line Items]
Interest rate	4.18%
Maturity date	Nov. 15, 2025
Series L Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 50,000	50,000
Series M Notes [Member]
Debt Instrument [Line Items]
Interest rate	1.12%
Maturity date	Sep. 23, 2026
Series M Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 45,470	46,437
Series N Notes [Member]
Debt Instrument [Line Items]
Interest rate	1.31%
Maturity date	Sep. 23, 2028
Series N Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 87,532	89,393
Series O Notes [Member]
Debt Instrument [Line Items]
Interest rate	1.57%
Maturity date	Sep. 23, 2031
Series O Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 48,882	49,921
Series P Notes [Member]
Debt Instrument [Line Items]
Interest rate	4.27%
Maturity date	May 30, 2025
Series P Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 85,000	85,000
Series R Notes [Member]
Debt Instrument [Line Items]
Interest rate	4.41%
Maturity date	May 30, 2029
Series R Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 75,000	75,000
Series S Notes [Member]
Debt Instrument [Line Items]
Interest rate	4.46%
Maturity date	May 30, 2030
Series S Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 75,000	75,000
Series T Notes [Member]
Debt Instrument [Line Items]
Interest rate	4.61%
Maturity date	May 30, 2033
Series T Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 80,000	80,000
Series Q Notes [Member]
Debt Instrument [Line Items]
Interest rate	4.35%
Maturity date	May 30, 2027
Series Q Notes [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 85,000	85,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maturity date	Jun. 19, 2024
Long-term debt	$ 181,852	$ 116,541
Revolving Credit Facility [Member] \| Minimum [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Variable interest rate	0.875%
Revolving Credit Facility [Member] \| Maximum [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Variable interest rate	1.75%

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6036836-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateEffectivePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

+ Details

Name:	us-gaap_DebtInstrumentMaturityDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28555-108399

+ Details

Name:	us-gaap_DeferredFinanceCostsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

+ Details

Name:	us-gaap_LongTermDebtCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ Details

Name:	us-gaap_LongTermDebtNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant