Long-term Debt (Schedule of Long-term Debt) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended	15 Months Ended
Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2015
Long-term debt balance	$ 887,000	$ 850,000	$ 887,000
Current portion of long-term debt	(100,000)	0	(100,000)
Short-term Debt	100,000	2,430	100,000
Long-term debt, excluding current portion	787,000	850,000	787,000
Series C Notes [Member] \| Notes Payable to Banks [Member]
Long-term debt balance	$ 0	$ 50,000	$ 0
Interest rate	5.92%	5.92%	5.92%
Maturity date	Oct. 01, 2015	Oct. 01, 2015
Series D Notes [Member] \| Notes Payable to Banks [Member]
Long-term debt balance	$ 100,000	$ 100,000	$ 100,000
Interest rate	6.39%	6.39%	6.39%
Maturity date	Oct. 01, 2018	Oct. 01, 2018
Series E Notes [Member] \| Notes Payable to Banks [Member]
Long-term debt balance	$ 57,000	$ 57,000	$ 57,000
Interest rate	7.81%	7.81%	7.81%
Maturity date	Apr. 03, 2016	Apr. 03, 2016
Series F Notes [Member] \| Notes Payable to Banks [Member]
Long-term debt balance	$ 43,000	$ 43,000	$ 43,000
Interest rate	8.24%	8.24%	8.24%
Maturity date	Apr. 03, 2019	Apr. 03, 2019
Series J Notes [Member]
Variable interest rate	1.62%		1.62%
Series J Notes [Member] \| Notes Payable to Banks [Member]
Long-term debt balance	$ 50,000	$ 50,000	$ 50,000
Variable Rate Basis			LIBOR
Basis Spread On Variable Rate	1.25%	1.25%
Maturity date	Nov. 15, 2020	Nov. 15, 2020
Series G Notes [Member] \| Notes Payable to Banks [Member]
Long-term debt balance	$ 50,000	$ 50,000	$ 50,000
Interest rate	3.42%	3.42%	3.42%
Maturity date	Nov. 15, 2020	Nov. 15, 2020
Series H Notes [Member] \| Notes Payable to Banks [Member]
Long-term debt balance	$ 25,000	$ 25,000	$ 25,000
Interest rate	4.03%	4.03%	4.03%
Maturity date	Nov. 15, 2023	Nov. 15, 2023
Series I Notes [Member] \| Notes Payable to Banks [Member]
Long-term debt balance	$ 25,000	$ 25,000	$ 25,000
Interest rate	4.18%	4.18%	4.18%
Maturity date	Nov. 15, 2025	Nov. 15, 2025
Series K Notes [Member] \| Notes Payable to Banks [Member]
Long-term debt balance	$ 50,000	$ 50,000	$ 50,000
Interest rate	4.03%	4.03%	4.03%
Maturity date	Nov. 15, 2023	Nov. 15, 2023
Series L Notes [Member] \| Notes Payable to Banks [Member]
Long-term debt balance	$ 50,000	$ 50,000	$ 50,000
Interest rate	4.18%	4.18%	4.18%
Maturity date	Nov. 15, 2025	Nov. 15, 2025
Revolving Credit Facility [Member]
Long-term debt balance	$ 437,000	$ 350,000	$ 437,000
Revolving Credit Agreement [Member]
Variable Rate Basis	LIBOR
Credit facility effective interest rate on outstanding borrowing	1.67%	1.44%	1.67%
Maturity date	Apr. 01, 2020
Short-term Debt	$ 100,000		$ 100,000
Revolving Credit Agreement [Member] \| Minimum [Member]
Basis Spread On Variable Rate	0.85%
Revolving Credit Agreement [Member] \| Maximum [Member]
Basis Spread On Variable Rate	1.65%
Chinese Credit Facility, RMB Denominated Loan [Member]
Variable Rate Basis	interest at the prevailing interest rate offered by the People's Bank of China on the date of borrowing, plus a margin equal to 15% of that prevailing rate
Chinese Credit Facility, USD Denominated Loan [Member]
Variable Rate Basis	interest at the lender's cost of borrowing rate at the date of borrowing, plus 3%

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

No definition available.

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- Definition

Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 20
-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 16
-Article 9

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- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

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/presentationRef
-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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

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- Definition

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

+ References

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- Definition

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

+ References

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- Definition

The effective interest rate at the end of the reporting period.

+ References

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- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, excluding amounts to be repaid within one year or the normal operating cycle, if longer (current maturities). Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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- Definition

Sum of the carrying values as of the balance sheet date of the portions of all long-term notes and loans payable due within one year or the operating cycle if longer.

+ References

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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-Topic 210
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Number 210
-Section 03
-Paragraph 13
-Subparagraph 2, 3
-Article 9

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