Derivatives (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 12,908		$ 12,908
Description of Derivative Activity Volume			Information related to the volume of activity for our interest rate derivative instruments subsequent to December 31, 2012 is as follows:(amounts in thousands)Interest Rate Swaps Eurodollar FuturesNotional amount as of December 31, 2012:$1,462,000 $—Additions:380,000 22,100,000Settlements, terminations, or expirations:(150,000) (1,850,000)Notional amount as of September 30, 2013:(1)$1,692,000 $20,250,000(1)The Eurodollar futures notional amount as of September 30, 2013 represents the total notional of the 3-month contracts with expiration dates from 2013 to 2020. The maximum notional outstanding for any 3-month period does not exceed $1,275,000.
Gain on derivative instruments, net	(24,019)	(333)	(12,683)	(907)
Derivative Liability, Notional Amount	21,517,000		21,517,000		1,462,000
Derivative Liabilities	(20,837)		(20,837)		(42,537)
Interest Rate Swap [Member]
Derivative [Line Items]
Notional Amount of Derivative Instruments Added			380,000
Notional Amount of Derivative Instruments Terminated			(150,000)
Eurodollar Future [Member]
Derivative [Line Items]
Notional Amount of Derivative Instruments Added			22,100,000
Notional Amount of Derivative Instruments Terminated			(1,850,000)
Interest Rate Swap [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments Held for Trading Purposes, Net	(6,225)	(333)	5,111	(907)
Derivative Liability, Notional Amount					1,462,000
Weighted-average Fixed Rate Swapped	1.64%		1.64%
Interest Rate Swap [Member] | Hedging instrument [Member]
Derivative [Line Items]
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value					(39,813)
Derivative Liability, Notional Amount					1,435,000
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	12,908		12,908
Derivative Asset, Notional Amount	425,000		425,000
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	(20,837)		(20,837)		(2,724)
Derivative Liability, Notional Amount	1,267,000		1,267,000		27,000
Derivative, Notional Amount	1,692,000		1,692,000
Eurodollar Future [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments Held for Trading Purposes, Net	(17,794)	0	(17,794)	0
Eurodollar Future [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Liability, Notional Amount	20,250,000		20,250,000
Derivative, Notional Amount	20,250,000		20,250,000
Forward Contracts [Member]
Derivative [Line Items]
Derivative, Notional Amount	150,000		150,000
Weighted-average Fixed Rate Swapped	2.17%		2.17%
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%
Interest Rate Swap Agreements, Maturities in Next 13-24 Months [Member] [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	130,000		130,000
Weighted-average Fixed Rate Swapped	2.06%		2.06%
Interest Rate Swap Agreements, Maturities in Next 25-36 Months [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	260,000		260,000
Weighted-average Fixed Rate Swapped	1.96%		1.96%
Interest Rate Swap Agreements, Maturities in Next 37-48 Months [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	212,000		212,000
Weighted-average Fixed Rate Swapped	0.01%		0.01%
Interest Rate Swap Agreements, Maturities in Next 49-60 Months [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	15,000		15,000
Weighted-average Fixed Rate Swapped	2.17%		2.17%
Interest Rate Swap Agreements, Maturities in Next 61-72 Months [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	385,000		385,000
Weighted-average Fixed Rate Swapped	1.58%		1.58%
Interest Rate Swap Agreements, Maturities in Next 73-84 Months [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	25,000		25,000
Weighted-average Fixed Rate Swapped	1.61%		1.61%
Interest Rate Swap Agreements, Maturities in Next 109-127 Months [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 230,000		$ 230,000
Weighted-average Fixed Rate Swapped	2.27%		2.27%