Derivatives (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	$ 11,137		$ 6,681
Derivative assets	12,064		18,488
Derivative Liabilities	(11,137)		(6,681)
Description of Derivative Activity Volume	The following table summarizes activity related to derivative instruments for the periods indicated:(amounts in thousands)Interest Rate Swaps Eurodollar FuturesNotional amount as of December 31, 2013$790,000 $9,000,000Additions75,000 —Settlements, terminations, or expirations(15,000) —Notional amount as of March 31, 2014(1)$850,000 $9,000,000(1)The Eurodollar futures notional amount as of March 31, 2014 represents the total notional of the 3-month contracts with expiration dates from 2016 to 2020. The maximum notional outstanding for any future 3-month period does not exceed $1,175,000.
Loss on derivative instruments, net	(13,422)	(17)
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative assets	12,064		18,488
Derivative Asset, Notional Amount	525,000		575,000
Derivative Liabilities	(11,137)		(6,681)
Derivative Liability, Notional Amount	9,325,000		9,215,000
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount			790,000
Gain (Loss) on Derivative Instruments Held for Trading Purposes, Net	(9,008)	(17)
Weighted-average Fixed Rate Swapped	1.61%
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	(1,378)		(1,336)
Derivative Liability, Notional Amount	325,000		215,000
Derivative, Notional Amount	850,000
Eurodollar Future [Member]
Derivative [Line Items]
Derivative, Notional Amount			9,000,000
Notional Amount of Derivative Instruments Added	0
Notional Amount of Derivative Instruments Terminated	0
Gain (Loss) on Derivative Instruments Held for Trading Purposes, Net	(4,414)	0
Eurodollar Future [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	(9,759)		(5,345)
Derivative Liability, Notional Amount	9,000,000		9,000,000
Derivative, Notional Amount	9,000,000
Interest Rate Swap Agreements, Maturities in Next 37-48 Months [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	185,000
Weighted-average Fixed Rate Swapped	0.92%
Interest Rate Swap Agreements, Maturities in Next 49-60 Months [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	350,000
Weighted-average Fixed Rate Swapped	1.62%
Interest Rate Swap Agreements, Maturities in Next 61-72 Months [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	35,000
Weighted-average Fixed Rate Swapped	1.24%
Interest Rate Swap Agreements, Maturities in Next 73-84 Months [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	100,000
Weighted-average Fixed Rate Swapped	2.08%
Interest Rate Swap Agreements, Maturities in Next 109-127 Months [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	180,000
Weighted-average Fixed Rate Swapped	2.13%
Interest Rate Swap [Member]
Derivative [Line Items]
Notional Amount of Derivative Instruments Added	75,000
Notional Amount of Derivative Instruments Terminated	$ 15,000