Derivatives (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2015		Sep. 30, 2014	Sep. 30, 2015		Sep. 30, 2014	Dec. 31, 2014
Derivative [Line Items]
Derivative assets, fair value							$ 5,727
Derivative assets, aggregate notional amount	$ 375,000			$ 375,000			440,000
Derivative liabilities, fair value	(63,708)			(63,708)			(35,898)
Derivative liabilities, aggregate notional amount	9,265,000			9,265,000			17,085,000
Derivative assets	10,057			10,057			5,727
Beginning of period notional amount				17,525,000
Notional Amount of Derivative Instruments Added				3,135,000
Notional Amount of Derivative Instruments Terminated				(11,020,000)
End of period notional amount	9,640,000			9,640,000
(Loss) gain on derivative instruments, net	(52,749)		$ 4,842	(60,982)		$ (31,654)
Forward Contracts [Member]
Derivative [Line Items]
End of period notional amount	$ 1,675,000			$ 1,675,000
Weighted-average Fixed Pay Rate	1.38%			1.38%
Weighted-average Fixed Receive Rate	1.38%			1.38%
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative assets, fair value	$ 10,057			$ 10,057			5,727
Derivative assets, aggregate notional amount	375,000			375,000			440,000
Derivative liabilities, fair value	(30,632)			(30,632)			(3,002)
Derivative liabilities, aggregate notional amount	2,965,000			2,965,000			485,000
Eurodollar Future [Member]
Derivative [Line Items]
Derivative assets, fair value	0			0			0
Derivative assets, aggregate notional amount	0	[1]		0	[1]		0	[2]
Derivative liabilities, fair value	(33,076)			(33,076)			(32,896)
Derivative liabilities, aggregate notional amount	6,300,000	[1]		6,300,000	[1]		$ 16,600,000	[2]
Beginning of period notional amount				16,600,000
Notional Amount of Derivative Instruments Added				0
Notional Amount of Derivative Instruments Terminated				(10,300,000)
End of period notional amount	6,300,000			6,300,000
(Loss) gain on derivative instruments, net	(11,027)		3,857	(24,942)		(11,937)
Receive-fixed interest rate swap [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Beginning of period notional amount				275,000
Notional Amount of Derivative Instruments Added				50,000
Notional Amount of Derivative Instruments Terminated				0
End of period notional amount	325,000			325,000
(Loss) gain on derivative instruments, net	6,975		339	9,757		339
Receive-fixed interest rate swap [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 13-24 Months [Member]
Derivative [Line Items]
End of period notional amount	$ 0			$ 0
Weighted-average Fixed Pay Rate	0.00%			0.00%
Weighted-average Fixed Receive Rate	0.00%			0.00%
Receive-fixed interest rate swap [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 37-48 Months [Member]
Derivative [Line Items]
End of period notional amount	$ 250,000			$ 250,000
Weighted-average Fixed Pay Rate	1.14%			1.14%
Weighted-average Fixed Receive Rate	1.14%			1.14%
Receive-fixed interest rate swap [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 49-60 Months [Member]
Derivative [Line Items]
End of period notional amount	$ 50,000			$ 50,000
Weighted-average Fixed Pay Rate	1.75%			1.75%
Weighted-average Fixed Receive Rate	1.75%			1.75%
Receive-fixed interest rate swap [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 73-84 Months [Member]
Derivative [Line Items]
End of period notional amount	$ 0			$ 0
Weighted-average Fixed Pay Rate	0.00%			0.00%
Weighted-average Fixed Receive Rate	0.00%			0.00%
Receive-fixed interest rate swap [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 85-96 Months [Member]
Derivative [Line Items]
End of period notional amount	$ 0			$ 0
Weighted-average Fixed Pay Rate	0.00%			0.00%
Weighted-average Fixed Receive Rate	0.00%			0.00%
Receive-fixed interest rate swap [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 97-108 Months [Member]
Derivative [Line Items]
End of period notional amount	$ 25,000			$ 25,000
Weighted-average Fixed Pay Rate	2.71%			2.71%
Weighted-average Fixed Receive Rate	2.71%			2.71%
Receive-fixed interest rate swap [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 109-120 Months [Member]
Derivative [Line Items]
End of period notional amount	$ 0			$ 0
Weighted-average Fixed Pay Rate	0.00%			0.00%
Weighted-average Fixed Receive Rate	0.00%			0.00%
Pay-fixed interest rate swap [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Beginning of period notional amount				$ 650,000
Notional Amount of Derivative Instruments Added				3,085,000
Notional Amount of Derivative Instruments Terminated				(720,000)
End of period notional amount	$ 3,015,000			3,015,000
(Loss) gain on derivative instruments, net	(48,697)		$ 646	(45,797)		$ (20,056)
Pay-fixed interest rate swap [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 13-24 Months [Member]
Derivative [Line Items]
End of period notional amount	$ 1,435,000			$ 1,435,000
Weighted-average Fixed Pay Rate	1.18%			1.18%
Weighted-average Fixed Receive Rate	1.18%			1.18%
Pay-fixed interest rate swap [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 37-48 Months [Member]
Derivative [Line Items]
End of period notional amount	$ 160,000			$ 160,000
Weighted-average Fixed Pay Rate	1.37%			1.37%
Weighted-average Fixed Receive Rate	1.37%			1.37%
Pay-fixed interest rate swap [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 49-60 Months [Member]
Derivative [Line Items]
End of period notional amount	$ 635,000			$ 635,000
Weighted-average Fixed Pay Rate	1.74%			1.74%
Weighted-average Fixed Receive Rate	1.74%			1.74%
Pay-fixed interest rate swap [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 73-84 Months [Member]
Derivative [Line Items]
End of period notional amount	$ 75,000			$ 75,000
Weighted-average Fixed Pay Rate	1.77%			1.77%
Weighted-average Fixed Receive Rate	1.77%			1.77%
Pay-fixed interest rate swap [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 85-96 Months [Member]
Derivative [Line Items]
End of period notional amount	$ 125,000			$ 125,000
Weighted-average Fixed Pay Rate	1.98%			1.98%
Weighted-average Fixed Receive Rate	1.98%			1.98%
Pay-fixed interest rate swap [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 97-108 Months [Member]
Derivative [Line Items]
End of period notional amount	$ 0			$ 0
Weighted-average Fixed Pay Rate	0.00%			0.00%
Weighted-average Fixed Receive Rate	0.00%			0.00%
Pay-fixed interest rate swap [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 109-120 Months [Member]
Derivative [Line Items]
End of period notional amount	$ 585,000			$ 585,000
Weighted-average Fixed Pay Rate	2.72%			2.72%
Weighted-average Fixed Receive Rate	2.72%			2.72%

[1] The Eurodollar futures aggregate notional amount represents the total notional of the 3-month contracts with expiration dates from 2017 to 2020. The maximum notional outstanding for any future 3-month period did not exceed $725,000 as of September 30, 2015

[2] The Eurodollar futures aggregate notional amount represents the total notional of the 3-month contracts with expiration dates from 2015 to 2020. The maximum notional outstanding for any future 3-month period did not exceed $1,300,000 as of December 31, 2014.