Secured Debt Agreements, Net - Additional Information (Detail)	3 Months Ended		9 Months Ended	12 Months Ended
	Dec. 31, 2020 USD ($) Lenders	Jun. 30, 2020 USD ($) Lenders	Dec. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Revolving credit agreement outstanding amount	$ 7,896,863,000		$ 9,753,059,000	$ 7,896,863,000	$ 9,753,059,000
Weighted-average advance rate				100.00%
Interest expense				$ 347,471,000	458,503,000	$ 359,625,000
Covenants, minimum tangible net worth	$ 3,000,000,000.0			$ 3,000,000,000.0
Covenants, percentage of tangible assets on cash proceeds from equity issuances				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				1.40%
Covenants, minimum cash liquidity amount	$ 10,000,000.0			$ 10,000,000.0
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Revolving credit agreement outstanding amount	0		0	0	0
Interest expense			2,600,000	1,600,000
Amortization of deferred fees and expenses			1,000,000.0	685,000,000,000
Revolving Credit Facility [Member] | Weighted Average [Member]
Debt Instrument [Line Items]
Revolving credit agreement weighted average outstanding amount			14,300,000
Revolving Credit Facility [Member] | Barclays [Member]
Debt Instrument [Line Items]
Maximum Facility Size	$ 250,000,000.0			250,000,000.0
Credit Facilities [Member]
Debt Instrument [Line Items]
Number of lenders | Lenders	7	7
Additional credit capacity		$ 7,900,000,000
Revolving credit agreement weighted average outstanding amount				8,800,000,000	8,800,000,000
Revolving credit agreement outstanding amount	$ 7,896,863,000		9,800,000,000	$ 7,896,863,000	$ 9,800,000,000
Basis spread on debt obligation, in percent					1.60%
Weighted-average advance rate				72.80%	79.40%
Weighted-average future funding period				3 years	3 years 7 months 6 days
Credit Facilities [Member] | Maximum [Member]
Debt Instrument [Line Items]
Additional credit capacity				$ 650,000,000.0
Credit Facilities [Member] | Barclays [Member]
Debt Instrument [Line Items]
Revolving credit agreement outstanding amount	$ 1,249,415,000		$ 1,442,083,000	$ 1,249,415,000	$ 1,442,083,000
LIBOR [Member] | Credit Facilities [Member] | Weighted-Average Cash Coupon [Member]
Debt Instrument [Line Items]
Basis spread on debt obligation, in percent				1.63%
LIBOR [Member] | Credit Facilities [Member] | Weighted-Average All-in Cost of Credit [Member]
Debt Instrument [Line Items]
Basis spread on debt obligation, in percent				1.83%	1.79%