Secured Debt Agreements - Additional Information (Detail)		3 Months Ended				6 Months Ended	9 Months Ended			12 Months Ended
	Sep. 30, 2016 USD ($) ExtensionOptions	Sep. 30, 2016 USD ($) ExtensionOptions	Jun. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($) ExtensionOptions	Jun. 30, 2016 USD ($)	Sep. 30, 2016 USD ($) ExtensionOptions	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Debt Instrument [Line Items]
Maturity date							Feb. 28, 2017
Secured debt agreements borrowings outstanding	$ 5,320,358,000	$ 5,320,358,000					$ 5,320,358,000	$ 6,116,105,000		$ 6,116,105,000
Interest expense		45,373,000		$ 51,329,000			139,819,000		$ 106,125,000
Secured debt agreements borrowings outstanding	5,335,908,000	5,335,908,000					5,335,908,000	6,131,751,000		6,131,751,000
Covenants, minimum tangible net worth	$ 1,900,000,000	$ 1,900,000,000					$ 1,900,000,000
Covenants, percentage of tangible assets on cash proceeds from equity issuances							75.00%
Covenants, percentage of recourse indebtedness	5.00%	5.00%					5.00%
Maximum [Member]
Debt Instrument [Line Items]
Covenants, indebtedness to total assets, in percent	83.33%	83.33%					83.33%
Minimum [Member]
Debt Instrument [Line Items]
Covenants, EBITDA to fixed charges, in percent							140.00%
Covenants, minimum cash liquidity amount	$ 10,000,000	$ 10,000,000					$ 10,000,000
Asset-Specific Financings [Member]
Debt Instrument [Line Items]
Weighted-average outstanding balance							557,900,000	574,300,000
Revolving Repurchase Facilities [Member]
Debt Instrument [Line Items]
Weighted-average outstanding balance							2,900,000,000	2,500,000,000
Aggregate borrowings	3,000,000,000	3,000,000,000					$ 3,000,000,000	2,500,000,000		$ 2,500,000,000
Weighted-average advance rate							79.10%			78.80%
Weighted-average initial maturity							1 year 4 months 24 days			1 year 3 months 18 days
Maximum Facility Size	5,523,080,000	5,523,080,000					$ 5,523,080,000	4,332,267,000		$ 4,332,267,000
Amount available for potential future fundings of loan	591,187,000	591,187,000					591,187,000	487,028,000		487,028,000
Current borrowing capacity	3,635,621,000	3,635,621,000					3,635,621,000	2,982,833,000		2,982,833,000
Secured debt agreements borrowings outstanding	3,044,434,000	3,044,434,000					$ 3,044,434,000	2,495,805,000		2,495,805,000
Revolving Repurchase Facilities [Member] | Wells Fargo [Member]
Debt Instrument [Line Items]
Weighted-average advance rate							79.60%
Maximum Facility Size	2,000,000,000	2,000,000,000					$ 2,000,000,000	1,000,000,000		1,000,000,000
Amount available for potential future fundings of loan	283,882,000	283,882,000					$ 283,882,000	124,818,000		124,818,000
Borrowings maturity term							Term matched
Current borrowing capacity	1,085,153,000	1,085,153,000					$ 1,085,153,000	687,200,000		687,200,000
GE Portfolio Acquisition Facility [Member]
Debt Instrument [Line Items]
Secured debt agreements borrowings outstanding	1,587,822,000	1,587,822,000					1,587,822,000	3,161,291,000		3,161,291,000
GE Portfolio Acquisition Facility [Member] | Sequential Repay Advance [Member]
Debt Instrument [Line Items]
Term of maturity date					1 year
Secured debt agreements borrowings outstanding								40,700,000		40,700,000
Current borrowing capacity					$ 237,200,000
Percentage of additional advance					5.00%
Sequential Repay Advance, percentage of guarantee rate					100.00%
GE Portfolio Acquisition Facility [Member] | Wells Fargo [Member]
Debt Instrument [Line Items]
Maximum Facility Size	1,800,000,000	1,800,000,000					1,800,000,000
Approximate credit line, outstanding amount	1,600,000,000
Amount available for potential future fundings of loan	200,500,000	200,500,000					$ 200,500,000
Additional credit capacity			$ 125,000,000
GE Portfolio Acquisition Facility [Member] | Asset Specific Borrowings [Member]
Debt Instrument [Line Items]
Weighted average rate					80.00%
Maturity date							May 20, 2020
Borrowings maturity term							The asset-specific borrowings are term matched to the underlying collateral assets with an outside maturity date of May 20, 2020, which may be extended pursuant to two one-year extension options.
Number of extension options | ExtensionOptions					2
Term of maturity date					1 year
Secured debt agreements borrowings outstanding	1,600,000,000	1,600,000,000					$ 1,600,000,000	$ 3,100,000,000		$ 3,100,000,000
GE Portfolio Acquisition Facility [Member] | Asset Specific Borrowings [Member] | Maximum [Member]
Debt Instrument [Line Items]
Percentage of guarantee rate					25.00%
Guarantee of outstanding borrowings					$ 250,000,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Weighted-average outstanding balance		24,500,000					29,700,000
Interest expense		421,000,000					915,000,000
Amortization of deferred fees and expenses		127,000,000					248,000,000
Secured debt agreements borrowings outstanding	$ 50,000,000	$ 50,000,000					$ 50,000,000
Revolving Credit Facility [Member] | Barclays [Member]
Debt Instrument [Line Items]
Maximum Facility Size			$ 125,000,000			$ 125,000,000
Number of extension options | ExtensionOptions	2	2					2
Term of maturity date							1 year
First mortgage bridge to term financing maximum period						6 months
Base Rate [Member] | GE Portfolio Acquisition Facility [Member] | Asset Specific Borrowings [Member] | Primary [Member]
Debt Instrument [Line Items]
Basis spread on debt obligation, in percent					1.75%
Base Rate [Member] | GE Portfolio Acquisition Facility [Member] | Asset Specific Borrowings [Member] | Primary [Member] | Year Four [Member]
Debt Instrument [Line Items]
Basis spread on debt obligation, in percent					1.80%
Base Rate [Member] | GE Portfolio Acquisition Facility [Member] | Asset Specific Borrowings [Member] | Primary [Member] | Year Five [Member]
Debt Instrument [Line Items]
Basis spread on debt obligation, in percent					1.85%
LIBOR [Member] | Revolving Repurchase Facilities [Member] | Wells Fargo [Member]
Debt Instrument [Line Items]
Basis spread on debt obligation, in percent							1.77%
LIBOR [Member] | Revolving Repurchase Facilities [Member] | Weighted-Average Cash Coupon [Member]
Debt Instrument [Line Items]
Basis spread on debt obligation, in percent							1.82%			1.83%
LIBOR [Member] | Revolving Repurchase Facilities [Member] | Weighted-Average All-in Cost of Credit [Member]
Debt Instrument [Line Items]
Basis spread on debt obligation, in percent							2.01%			2.05%
LIBOR [Member] | GE Portfolio Acquisition Facility [Member] | Sequential Repay Advance [Member]
Debt Instrument [Line Items]
Basis spread on debt obligation, in percent					3.10%
LIBOR basis spread on debt obligation							30-day LIBOR