Debt Obligations - Additional Information (Detail)	3 Months Ended	6 Months Ended		0 Months Ended	6 Months Ended	0 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
	Jun. 30, 2014 USD ($)	Jun. 30, 2014 USD ($) Facility Assets	Dec. 31, 2013 USD ($)	Nov. 30, 2013 Convertible Senior Notes [Member] USD ($)	Jun. 30, 2014 Convertible Senior Notes [Member] USD ($)	Nov. 30, 2013 Convertible Senior Notes [Member] Class A Common Stock [Member] USD ($)	Jun. 30, 2014 Maximum [Member]	Jun. 30, 2014 Minimum [Member] USD ($)	Jun. 30, 2014 Goldman Sachs [Member] USD ($)	Apr. 25, 2014 Goldman Sachs [Member] Maximum [Member]	Jun. 30, 2014 Wells Fargo [Member] USD ($)	Jun. 30, 2014 Wells Fargo [Member] Maximum [Member]	Jun. 30, 2014 Wells Fargo [Member] March 13, 2014 Credit Facility [Member]	Jun. 30, 2014 Wells Fargo [Member] July 30, 2013 Credit Facility [Member] USD ($)	Jun. 30, 2014 Wells Fargo [Member] June 7, 2013 Credit Facility [Member] USD ($)	Jun. 30, 2014 Wells Fargo [Member] July 8, 2013 Credit Facility [Member] USD ($)	Jun. 30, 2014 Morgan Stanley [Member] USD ($)	Jun. 30, 2014 Morgan Stanley [Member] GBP (£)	Jun. 30, 2014 Morgan Stanley [Member] Maximum [Member]	Jun. 30, 2014 JP Morgan [Member] USD ($)	Dec. 20, 2013 JP Morgan [Member] USD ($)	Dec. 20, 2013 JP Morgan [Member] GBP (£)	Dec. 20, 2013 JP Morgan [Member] Maximum [Member] Senior Mortgage Collateral [Member]	Dec. 20, 2013 JP Morgan [Member] Maximum [Member] Mezzanine and Junior Mortgage Collateral [Member]	Jun. 30, 2014 Citibank [Member] USD ($)	Jun. 30, 2014 Citibank [Member] First Tranche [Member] USD ($)	Jun. 12, 2013 Citibank [Member] Maximum [Member]	Jun. 30, 2014 Bank of America [Member] USD ($)	May 21, 2013 Bank of America [Member] Maximum [Member] Senior Mortgage Collateral [Member]	May 21, 2013 Bank of America [Member] Maximum [Member] Mezzanine and Junior Mortgage Collateral [Member]	Jun. 30, 2014 Weighted-Average Cash Coupon [Member]	Jun. 30, 2014 Weighted-Average All-in Cost of Credit [Member]	Jun. 30, 2014 MetLife [Member] USD ($)	Jun. 27, 2014 MetLife [Member] Maximum [Member]	Jun. 30, 2014 MetLife [Member] June 27, 2014 Credit Facility [Member]
Debt Instrument [Line Items]
Number of revolving repurchase facilities closed		3
Closing of asset specific repurchase facilities		1
Proceeds from line of credit		$ 1,600,000,000
Aggregate borrowings	1,500,000,000	1,500,000,000
Description of interest rate									LIBOR plus a margin of 2.75%		LIBOR plus 2.00%			LIBOR plus a margin of 2.25%	LIBOR plus 4.00%	LIBOR plus at 2.50%	Three-month LIBOR plus 2.32%	Three-month LIBOR plus 2.32%		LIBOR plus 2.02%					LIBOR plus 1.95%			LIBOR plus 1.78%			LIBOR plus 1.95% per annum	LIBOR plus 2.19% per annum	LIBOR plus 1.89%
LIBOR basis spread on debt obligation									2.75%		2.00%			2.25%	4.00%	2.50%	2.32%	2.32%		2.02%					1.95%			1.78%			1.95%	2.19%	1.89%
Weighted-average initial maturity		2 years 3 months 18 days
Weighted-average outstanding repurchase obligation	1,400,000,000	1,300,000,000
Facility size									194,400,000		500,000,000			59,800,000	32,000,000	88,300,000	425,900,000	250,000,000		250,000,000	260,700,000	153,000,000				500,000,000		500,000,000					500,000,000
Maturity period													Master repurchase agreement with Wells Fargo specifies a one-year availability period, during which new advances can be made and which availability period is renewable at the discretion of Wells Fargo.	The initial maturity date of the facility is August 8, 2015, which may be extended pursuant to three one-year extension options, each of which may be exercised by us.		The initial maturity date of the facility is June 7, 2016, which may be extended pursuant to (i) two one-year extension options, each of which may be exercised by us, and (ii) an additional one-year extension option, contingent upon notice regarding the failure of the collateral mortgage loan to be repaid at its final maturity.				Repurchase agreement with JP Morgan specifies an availability period ending on June 28, 2015, during which new advances can be made and which availability period is renewable at the discretion of JP Morgan.					The initial facility expiration date is June 12, 2017, which may be extended annually by us.			The initial maturity date of the facility is May 21, 2017, subject to two one-year extension options					2015-06-29		An initial facility expiration date is June 29, 2015, subject to five one-year extension options, each of which may be exercised at our option.
Outstanding borrowings	1,779,650,000	1,779,650,000	1,109,353,000								190,100,000						135,800,000			293,600,000					351,200,000			387,700,000					165,400,000
Maximum advance rate											77.00%						78.60%	78.60%		75.80%					75.60%			78.70%					77.00%
Percentage of recourse debt										50.00%		25.00%							25.00%				25.00%	100.00%			25.00%		50.00%	100.00%				50.00%
Master repurchase agreement, maturity date																	Mar. 03, 2017	Mar. 03, 2017		Dec. 20, 2016
Initial expiration period									Apr. 25, 2017
Covenants, EBITDA to fixed charges							1.40	1.0
Covenants, minimum tangible net worth	908,100,000	908,100,000
Covenants, percentage of tangible assets on cash proceeds from equity issuances		75.00%
Covenants, minimum cash liquidity amount								10,000,000
Covenants, percentage of recourse indebtedness	5.00%	5.00%
Covenants, indebtedness to total assets							83.33%
Convertible Senior Notes, Principal amount				172,500,000
Convertible Senior Notes, Interest rate				5.25%
Maturity Date					Dec. 01, 2018
Convertible Senior Notes, Interest rate including underwriter discounts				5.87%
Convertible notes, net	160,671,000	160,671,000	159,524,000		160,700,000
Discount upon issuance of Convertible Notes				9,100,000	8,200,000
Convertible Notes, debt conversion, common stock issued						34.8943
Convertible Notes, debt conversion, principal amount						$ 1,000
Debt instrument, conversion price						$ 28.66
Description of convertible notes conversion				The Convertible Notes are convertible at the holders' option, only under specific circumstances, into shares of our class A common stock prior to the close of business on August 31, 2018, at the applicable conversion rate in effect on the conversion date.
Convertible Notes, effective interest rate				6.50%
Convertible Senior Notes, Interest rate including amortization of discount upon issuance				7.16%