Derivatives (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013 Derivatives	Sep. 30, 2011	Jun. 30, 2013 Derivatives	Jun. 30, 2012	Dec. 31, 2012
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 14,860		$ 14,860		$ 0
Description of Derivative Activity Volume	180000
Derivative Asset, Notional Amount	600,000		600,000		0
Derivative Liabilities	21,192		21,192		42,537
Forward Contracts [Member]
Derivative [Line Items]
Derivative, Notional Amount	150,000		150,000
Weighted-average Fixed Rate Swapped	2.17%		2.17%
Interest rate swap [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	11,353	(500)	11,336	(574)
Derivative Liability, Notional Amount	1,042,000		1,042,000		1,462,000
Derivative Liabilities	(21,192)		(21,192)		(42,537)
Derivative, Notional Amount	1,642,000		1,642,000
Number of Swaps	46		46
Weighted-average Fixed Rate Swapped	1.61%		1.61%
Interest rate swap [Member] | Hedging instrument [Member]
Derivative [Line Items]
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value	0		0		(39,813)
Derivative Liability, Notional Amount	0		0		1,435,000
Interest rate swap [Member] | Designated as Trading [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	(21,192)		(21,192)		(2,724)
Derivative Liability, Notional Amount	1,042,000		1,042,000		27,000
Derivative, Notional Amount	1,642,000		1,642,000
0-12 months [Member] | Interest rate swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	435,000		435,000
Weighted-average Fixed Rate Swapped	1.26%		1.26%
0-12 months [Member] | Interest rate swap [Member] | Designated as Trading [Member]
Derivative [Line Items]
Derivative, Notional Amount	435,000		435,000
13-36 months [Member] | Interest rate swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	390,000		390,000
Weighted-average Fixed Rate Swapped	1.99%		1.99%
13-36 months [Member] | Interest rate swap [Member] | Designated as Trading [Member]
Derivative [Line Items]
Derivative, Notional Amount	390,000		390,000
37-60 months [Member] | Interest rate swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	212,000		212,000
Weighted-average Fixed Rate Swapped	1.17%		1.17%
37-60 months [Member] | Interest rate swap [Member] | Designated as Trading [Member]
Derivative [Line Items]
Derivative, Notional Amount	212,000		212,000
Over 60 months [Member] | Interest rate swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	605,000		605,000
Weighted-average Fixed Rate Swapped	1.76%		1.76%
Over 60 months [Member] | Interest rate swap [Member] | Designated as Trading [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 605,000		$ 605,000