Secured Debt Agreements - Additional Information (Detail)	3 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2015 USD ($) ExtensionOptions	Sep. 30, 2015 USD ($) Facility Assets	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Proceeds from line of credit		$ 256,000,000
Secured debt agreements borrowings outstanding		6,585,654,000	$ 2,365,336,000
Covenants, minimum tangible net worth		$ 1,900,000,000
Covenants, percentage of tangible assets on cash proceeds from equity issuances		75.00%
Covenants, percentage of recourse indebtedness		5.00%
Maximum [Member]
Debt Instrument [Line Items]
Covenants, EBITDA to fixed charges, in percent		1.40%
Covenants, indebtedness to total assets, in percent		83.33%
Minimum [Member]
Debt Instrument [Line Items]
Covenants, EBITDA to fixed charges, in percent		1.00%
Covenants, minimum cash liquidity amount		$ 10,000,000
Asset-Specific Repurchase Agreements [Member]
Debt Instrument [Line Items]
Proceeds from line of credit		103,100,000
Weighted-average outstanding balance		$ 379,000,000	257,900,000
Closing of asset specific repurchase facilities | Assets		1
Revolving Repurchase Facilities [Member]
Debt Instrument [Line Items]
Number of revolving repurchase facilities closed | Facility		3
Proceeds from line of credit		$ 1,200,000,000
Aggregate borrowings		$ 2,800,000,000
Weighted-average initial maturity		1 year 6 months
Weighted-average outstanding balance		$ 2,400,000,000
Approximate credit line amount		3,197,027,000
Amount available for potential future fundings of loan		416,822,000
Secured debt agreements borrowings outstanding		2,780,205,000	$ 2,040,783,000
Current borrowing capacity		$ 2,780,205,000
Revolving Repurchase Facilities [Member] | Wells Fargo [Member]
Debt Instrument [Line Items]
LIBOR basis spread on debt obligation, description		L+1.80 %
LIBOR basis spread on debt obligation, in percent		1.80%
Approximate credit line amount		$ 704,733,000
Amount available for potential future fundings of loan		$ 137,434,000
Borrowings maturity term		Term matched
Current borrowing capacity		$ 567,299,000
GE Portfolio Acquisition Facility [Member]
Debt Instrument [Line Items]
Approximate credit line, outstanding amount		3,600,000,000
Amount available for potential future fundings of loan		158,500,000
Secured debt agreements borrowings outstanding		3,570,131,000
GE Portfolio Acquisition Facility [Member] | Sequential Repay Advance [Member]
Debt Instrument [Line Items]
Term of maturity date	1 year
Secured debt agreements borrowings outstanding		134,000,000
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]
Approximate credit line amount		$ 3,700,000,000
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		$ 3,400,000,000
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
Weighted-Average Cash Coupon [Member] | Revolving Repurchase Facilities [Member]
Debt Instrument [Line Items]
LIBOR basis spread on debt obligation, description		LIBOR plus 1.83% per annum
LIBOR basis spread on debt obligation, in percent		1.83%
Weighted-Average All-in Cost of Credit [Member] | Revolving Repurchase Facilities [Member]
Debt Instrument [Line Items]
LIBOR basis spread on debt obligation, description		LIBOR plus 2.04% per annum
LIBOR basis spread on debt obligation, in percent		2.04%
Base Rate [Member] | GE Portfolio Acquisition Facility [Member] | Asset Specific Borrowings [Member] | Primary [Member]
Debt Instrument [Line Items]
LIBOR basis spread on debt obligation, description		The asset-specific borrowings are currency matched to the collateral assets and accrue interest at a rate equal to the sum of (i) the applicable base rate plus (ii) a margin of 1.75%, which will increase to 1.80% and 1.85% in year four and year five, respectively.
LIBOR 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]
LIBOR 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]
LIBOR basis spread on debt obligation, in percent	1.85%
LIBOR [Member] | GE Portfolio Acquisition Facility [Member] | Sequential Repay Advance [Member]
Debt Instrument [Line Items]
LIBOR basis spread on debt obligation, description		Accrue interest at a rate equal to the sum of (i) 30-day LIBOR plus (ii) a margin of 3.10%.
LIBOR basis spread on debt obligation, in percent	3.10%