Secured Debt Agreements, Net - Additional Information (Detail) € in Millions, £ in Millions		3 Months Ended						6 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($) ExtensionOptions	Mar. 31, 2017 USD ($) ExtensionOptions Facility	Mar. 31, 2017 GBP (£) Facility	Mar. 31, 2017 EUR (€) Facility	Dec. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)	Jun. 30, 2015 USD ($) ExtensionOptions	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Basis spread on debt obligation, in percent		1.90%	1.90%	1.90%
Weighted-average advance rate		78.90%	78.90%	78.90%
Secured debt agreements borrowings outstanding	$ 5,760,191,000	$ 5,760,191,000			$ 5,716,354,000				$ 5,716,354,000
Interest expense		46,674,000				$ 45,381,000
Secured debt agreements borrowings outstanding	5,776,165,000	5,776,165,000			5,731,626,000				5,731,626,000
Covenants, minimum tangible net worth	$ 1,900,000,000	$ 1,900,000,000
Covenants, percentage of tangible assets on cash proceeds from equity issuances		75.00%	75.00%	75.00%
Covenants, percentage of recourse indebtedness	5.00%	5.00%
Maximum [Member]
Debt Instrument [Line Items]
Covenants, indebtedness to total assets, in percent	83.33%	83.33%
Minimum [Member]
Debt Instrument [Line Items]
Covenants, EBITDA to fixed charges, in percent		140.00%	140.00%	140.00%
Covenants, minimum cash liquidity amount	$ 10,000,000	$ 10,000,000
Asset-Specific Financings [Member]
Debt Instrument [Line Items]
Weighted-average outstanding balance		696,400,000			606,900,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Weighted-average outstanding balance					35,300,000
Interest expense		240,000			506,000
Amortization of deferred fees and expenses		126,000			128,000
Secured debt agreements borrowings outstanding	$ 0	$ 0			0				0
Revolving Credit Facility [Member] | Barclays [Member]
Debt Instrument [Line Items]
Maximum Facility Size								$ 125,000,000
Number of extension options | ExtensionOptions	2	2
Term of maturity date		1 year	1 year	1 year
First mortgage bridge to term financing maximum period								6 months
GE Portfolio Acquisition Facility [Member]
Debt Instrument [Line Items]
Secured debt agreements borrowings outstanding	$ 1,250,524,000	$ 1,250,524,000			1,479,582,000				1,479,582,000
GE Portfolio Acquisition Facility [Member] | Wells Fargo [Member]
Debt Instrument [Line Items]
Maximum Facility Size	1,400,000,000	1,400,000,000
Approximate credit line, outstanding amount	1,300,000,000
Amount available for potential future fundings of loan	171,700,000	$ 171,700,000
GE Portfolio Acquisition Facility [Member] | Asset Specific Borrowings [Member]
Debt Instrument [Line Items]
Weighted average rate							80.00%
Maturity date		May 20, 2020	May 20, 2020	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.	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.	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	1,300,000,000	$ 1,300,000,000			1,500,000,000				1,500,000,000
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
Credit Facilities [Member]
Debt Instrument [Line Items]
Number of revolving repurchase facilities closed | Facility		2	2	2
Additional credit capacity			£ 250.0	€ 250.0
Weighted-average outstanding balance		$ 3,500,000,000			3,600,000,000
Aggregate borrowings	4,000,000,000	$ 4,000,000,000			2,900,000,000				$ 2,900,000,000
Weighted-average advance rate		78.90%	78.90%	78.90%					79.10%
Weighted-average initial maturity		1 year 6 months	1 year 6 months	1 year 6 months					1 year 6 months
Maximum Facility Size	6,569,880,000	$ 6,569,880,000			5,479,180,000				$ 5,479,180,000
Amount available for potential future fundings of loan	449,536,000	449,536,000			541,743,000				541,743,000
Secured debt agreements borrowings outstanding	3,958,064,000	3,958,064,000			3,572,837,000				3,572,837,000
Credit Facilities [Member] | Wells Fargo [Member]
Debt Instrument [Line Items]
Maximum Facility Size	2,000,000,000	2,000,000,000			2,000,000,000				2,000,000,000
Amount available for potential future fundings of loan	$ 229,312,000	$ 229,312,000			$ 232,209,000				$ 232,209,000
Borrowings maturity term		Term matched	Term matched	Term matched
Credit Facilities [Member] | Asset-Specific Financings [Member]
Debt Instrument [Line Items]
Additional credit capacity		$ 500,000,000
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] | Credit Facilities [Member] | Weighted-Average Cash Coupon [Member]
Debt Instrument [Line Items]
Basis spread on debt obligation, in percent		1.90%	1.90%	1.90%					1.82%
LIBOR [Member] | Credit Facilities [Member] | Weighted-Average All-in Cost of Credit [Member]
Debt Instrument [Line Items]
Basis spread on debt obligation, in percent		2.11%	2.11%	2.11%					2.02%