Derivative and Other Fair Value Instruments (Details 3) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Increase (Decrease) in Fair Value of Interest Rate Fair Value Hedging Instruments	$ 1,597	$ (1,523)	$ (7,448)
Increase (Decrease) in Fair Value of Hedged Item in Interest Rate Fair Value Hedge	(1,597)	1,523	7,448
Effective Portion - Amount of Gain/ (Loss) Recognized in OCI on Derivative	(33,215)	18,771	(11,772)
Effective Portion - Amount of Gain/ (Loss) Reclassified from Accumulated OCI into Income	(16,868)	(20,141)	(14,678)
Ineffective Portion - Amount of Gain/ (Loss) Reclassifed from Accumulated OCI into Income	91	0	0
Interest Rate Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Increase (Decrease) in Fair Value of Interest Rate Fair Value Hedging Instruments	1,597	(1,523)	(7,448)
Increase (Decrease) in Fair Value of Hedged Item in Interest Rate Fair Value Hedge	(1,597)	1,523	7,448
Derivative, Description of Hedged Item	Fixed rate debt	Fixed rate debt	Fixed rate debt
Forward Starting Swaps/Treasury Locks [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Effective Portion - Amount of Gain/ (Loss) Recognized in OCI on Derivative	(33,215)	18,771	(11,772)
Effective Portion - Amount of Gain/ (Loss) Reclassified from Accumulated OCI into Income	(16,868)	(20,141)	(14,678)
Ineffective Portion - Amount of Gain/ (Loss) Reclassifed from Accumulated OCI into Income	$ 91	$ 0	$ 0

Description of the hedged item related to the derivative. Includes the type of instrument hedged, contract amount, term, and so forth.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1

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The portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments representing (a) the amount of the hedge ineffectiveness and (b) the amount, if any, excluded from the assessment of hedge effectiveness.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624171-113959

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The effective portion of gains on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

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The effective portion of loss reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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Amount of unrealized gain (loss) included in earnings related to the fair value of the hedged item in an interest rate fair value hedge, offset by the gain (loss) on the hedging instrument to the extent that the fair value hedge is determined to be effective.

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Amount of unrealized gain (loss) related to the fair value of interest rate derivatives designated as fair value hedging instruments, as offset by the gain (loss) on the hedged item to the extent that the fair value hedge is determined to be effective.

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