Secured Financing Agreements (Details) (USD $)			3 Months Ended		6 Months Ended			6 Months Ended			6 Months Ended		6 Months Ended		6 Months Ended		6 Months Ended		6 Months Ended			6 Months Ended	0 Months Ended	6 Months Ended	0 Months Ended	1 Months Ended	6 Months Ended		6 Months Ended		6 Months Ended			6 Months Ended		6 Months Ended		6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 Secured financing agreements	Jun. 30, 2013 Secured financing agreements	Jun. 30, 2014 Secured financing agreements	Jun. 30, 2013 Secured financing agreements	Dec. 31, 2013 Secured financing agreements	Jun. 30, 2014 Lender 1 Repo 1 Facility	Jan. 27, 2014 Lender 1 Repo 1 Facility	Dec. 31, 2013 Lender 1 Repo 1 Facility	Jun. 30, 2014 Lender 1 Repo 1 Facility Minimum	Jan. 31, 2014 Lender 1 Repo 1 Facility Minimum	Jun. 30, 2014 Lender 1 Repo 1 Facility Maximum	Jan. 31, 2014 Lender 1 Repo 1 Facility Maximum	Jun. 30, 2014 Lender 1 Repo 2 Facility	Dec. 31, 2013 Lender 1 Repo 2 Facility	Jun. 30, 2014 Lender 1 Repo 3 Facility	Dec. 31, 2013 Lender 1 Repo 3 Facility	Jun. 30, 2014 Lender 2 Repo 1 Facility	Dec. 31, 2013 Lender 2 Repo 1 Facility	Jul. 24, 2014 Lender 2 Repo 1 Facility Subsequent event	Jun. 30, 2014 Lender 2 Repo 1 Facility Minimum	Jul. 24, 2014 Lender 2 Repo 1 Facility Minimum Subsequent event	Jun. 30, 2014 Lender 2 Repo 1 Facility Maximum	Jul. 24, 2014 Lender 2 Repo 1 Facility Maximum Subsequent event	May 31, 2014 Lender 3 Repo I item	Jun. 30, 2014 Lender 3 Repo I	Dec. 31, 2013 Lender 3 Repo I	Jun. 30, 2014 Conduit Repo 1 Facility	Dec. 31, 2013 Conduit Repo 1 Facility	Jun. 30, 2014 Conduit Repo 2 Facility	Jun. 30, 2014 Lender 4 Repo 1 Facility	Dec. 31, 2013 Lender 4 Repo 1 Facility	Jun. 30, 2014 Lender 5 Repo 1 Facility	Dec. 31, 2013 Lender 5 Repo 1 Facility	Jun. 30, 2014 Borrowing Base	Dec. 31, 2013 Borrowing Base	Jun. 30, 2014 Term Loan	Dec. 31, 2013 Term Loan
Debt Instrument:
Pricing rate, basis								LIBOR							LIBOR		LIBOR		LIBOR								LIBOR		LIBOR		LIBOR	LIBOR		LIBOR		LIBOR		LIBOR
Pricing margin (as a percent)											1.85%		5.25%		1.90%		2.75%					2.00%		2.75%			2.85%		2.20%		2.10%	2.60%		2.00%		3.25%		2.75%
Pledged Asset Carrying Value	$ 6,461,251,000							$ 1,349,733,000							$ 230,129,000		$ 210,041,000		$ 269,290,000								$ 135,132,000				$ 128,083,000	$ 456,758,000		$ 84,150,000		$ 661,164,000		$ 2,936,771,000
Maximum Facility Size	3,378,812,000							1,000,000,000	1,000,000,000						175,000,000		148,860,000		225,000,000		325,000,000						93,836,000		250,000,000		150,000,000	359,226,000		58,467,000		250,000,000		668,423,000
Carrying Value	2,561,267,000	2,257,560,000						753,032,000		449,323,000					120,627,000	127,943,000	148,860,000	154,133,000	181,151,000	100,886,000							93,836,000	50,871,000		129,843,000	95,568,000	359,226,000	347,697,000	58,467,000	58,467,000	84,386,000	169,104,000	666,114,000	669,293,000
Current maturity period, after which the buyer delivers notice to seller, subject to a maximum date of March 13, 2015															180 days
Debt instrument reduction in basis spread																							0.25%		0.50%
Floor interest rate (as a percent)																																						0.75%
Discount amortization																																						2,300,000	2,500,000
Available borrowings under the facility before amendment									550,000,000												225,000,000
Maximum liability guaranteed (as a percent)											25.00%	25.00%	100.00%	100.00%
Amount of increase in additional borrowings																										42,700,000
Number of extension options																										2
Extended term																										1 year
Repayment of secured financings
2014 (remainder of)			194,472,000		194,472,000												26,200,000														95,600,000			58,500,000
2015			155,464,000		155,464,000
2016			296,329,000		296,329,000
2017			568,760,000		568,760,000
2018			223,683,000		223,683,000
Thereafter			1,124,868,000		1,124,868,000
Total			2,563,576,000		2,563,576,000
Deferred financing costs, net of amortization			24,900,000		24,900,000		22,500,000
Additional non-cash interest expense			$ 2,600,000	$ 1,800,000	$ 5,300,000	$ 5,000,000