Secured Debt Agreements, Net - Additional Information (Detail) € in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) Facility	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2018 EUR (€)
Debt Instrument [Line Items]
Secured debt agreements borrowings outstanding		$ 38,456,000
Interest expense	$ 359,625,000	234,870,000	$ 184,270,000
Secured debt agreements borrowings outstanding	8,996,481,000	5,290,536,000
Covenants, minimum tangible net worth	$ 2,500,000,000
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	140.00%
Covenants, minimum cash liquidity amount	$ 10,000,000
Asset-Specific Financings [Member]
Debt Instrument [Line Items]
Weighted-average outstanding balance	1,300,000,000	576,400,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Weighted-average outstanding balance	44,300,000	30,700,000
Interest expense	3,800,000	3,000,000
Amortization of deferred fees and expenses	1,100,000	829,000
Secured debt agreements borrowings outstanding	43,845,000	0
Revolving Credit Facility [Member] | Barclays [Member]
Debt Instrument [Line Items]
Maximum Facility Size	$ 250,000,000
First mortgage bridge to term financing maximum period	6 months
Credit Facilities [Member]
Debt Instrument [Line Items]
Additional credit capacity	$ 2,000,000,000
Number of revolving repurchase facilities closed | Facility	5
Weighted-average outstanding balance	$ 4,700,000,000	4,068,249,000
Aggregate borrowings	$ 6,903,683,000	$ 4,068,249,000
Basis spread on debt obligation, in percent	1.75%
Weighted-average advance rate	79.30%	78.70%
Weighted-average initial maturity	1 year 9 months 18 days	1 year 6 months
Maximum Facility Size	$ 11,030,045,000	$ 7,155,975,000
Secured debt agreements borrowings outstanding	$ 6,903,683,000	$ 4,068,249,000
Credit Facilities [Member] | Joint Venture [Member]
Debt Instrument [Line Items]
Number of new credit facility | Facility	2
Additional credit capacity	$ 2,300,000,000
Credit Facilities [Member] | Barclays [Member]
Debt Instrument [Line Items]
Aggregate borrowings	890,620,000
Maximum Facility Size	$ 1,500,000,000
Asset-Specific Financings [Member]
Debt Instrument [Line Items]
Secured debt agreements borrowings outstanding | €				€ 800.0
Asset-Specific Financings [Member] | Senior Loan [Member]
Debt Instrument [Line Items]
Secured loan | €				€ 1,000.0
LIBOR [Member] | Credit Facilities [Member] | Weighted-Average Cash Coupon [Member]
Debt Instrument [Line Items]
Basis spread on debt obligation, in percent	1.75%	1.90%
LIBOR [Member] | Credit Facilities [Member] | Weighted-Average All-in Cost of Credit [Member]
Debt Instrument [Line Items]
Basis spread on debt obligation, in percent	1.95%	2.12%