Notes Payable Callable debt (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Year Two	$ 1,679,364	$ 937,690
Long-term Debt, Weighted Average Interest Rate	1.99%	2.41%
Long-term Debt, Maturities, Repayments of Principal in Year Three	1,128,413	1,277,938
Long-term Debt, Maturities, Repayments of Principal in Year Four	863,799	632,905
Long-term Debt, Maturities, Repayments of Principal in Year Five	616,187	760,772
Long-term Debt, Maturities, Repayments of Principal after Year Five	746,976	495,577
Long-term Debt, Excluding Current Maturities	5,034,739	4,104,882
Call Option [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Year Two	63,977
Long-term Debt, Weighted Average Interest Rate	1.08%
Long-term Debt, Maturities, Repayments of Principal in Year Three	206,820
Long-term Debt, Maturities, Repayments of Principal in Year Four	33,970
Long-term Debt, Maturities, Repayments of Principal in Year Five	256,798
Long-term Debt, Maturities, Repayments of Principal after Year Five	169,533
Long-term Debt, Excluding Current Maturities	$ 731,098
Due year two [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	2.36%	1.11%
Due year two [Member] \| Call Option [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	0.29%
Due year three [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	1.40%	3.09%
Due year three [Member] \| Call Option [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	0.48%
Due year four [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	1.74%	2.21%
Due year four [Member] \| Call Option [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	0.59%
Due year five [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	1.19%	2.10%
Due year five [Member] \| Call Option [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	0.91%
Due after five years [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	2.97%	3.84%
Due after five years [Member] \| Call Option [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	2.46%

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. 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/presentationRef

-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

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 9

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 7

Reference 4: http://www.xbrl.org/2003/role/presentationRef

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-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 20, 22

-Article 5

Reference 5: 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

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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Amount of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates maturing after the fifth fiscal year following the latest fiscal year.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 47

-Paragraph 10

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Amount of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates maturing in the fifth fiscal year following the latest fiscal year.

+ References

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Amount of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates maturing in the fourth fiscal year following the latest fiscal year.

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Amount of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates maturing in the third fiscal year following the latest fiscal year.

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Amount of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates maturing in the second fiscal year following the latest fiscal year.

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Reflects the calculation as of the balance sheet date of the average interest rate weighted by the amount of long-term debt outstanding by type or by instrument at that time.

+ References

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