Secured Debt and Unsecured Debt (Details 3) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Aggregate maturities of debt
2013	$ 520,934
2014	248,881
2015	395,274
2016	874,199
2017	316,438
Thereafter	1,227,379
Total Debt	3,583,105us-gaap_LongTermDebt	3,523,703us-gaap_LongTermDebt
Secured Debt
Aggregate maturities of debt
2013	196,648
2014	166,504
2015	242,774
2016	225,756
2017	316,438
Thereafter	213,409
Total Debt	1,361,529
Secured Debt \| Fixed Rate Debt
Aggregate maturities of debt
2013	196,648
2014	135,167
2015	177,774
2016	120,969
2017	248,738
Thereafter	90,000
Total Debt	969,296
Secured Debt \| Variable Rate Debt
Aggregate maturities of debt
2013	0
2014	31,337
2015	65,000
2016	104,787
2017	67,700
Thereafter	123,409
Total Debt	392,233
Unsecured Debt
Aggregate maturities of debt
2013	324,286
2014	82,377
2015	152,500
2016	648,443
2017	0
Thereafter	1,013,970
Total Debt	$ 2,221,576

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.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 7

Reference 2: 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 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

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-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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

-Publisher SEC

-Name Regulation S-X (SX)

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-Article 9

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 20, 22

-Article 5

Reference 6: http://www.xbrl.org/2003/role/presentationRef

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-Section S99

-Paragraph 1

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ 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

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 3

-Subparagraph (SX 210.12-04.(a))

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