Secured Debt, Net - Schedule of All in Cost of Secured Credit Facilities (Detail) - Credit Facilities [Member] - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Schedule Of All In Cost Of Secured Credit Facilities [Line Items]
New Financings	$ 5,279,550	$ 898,516
Total Borrowings	$ 11,188,855	$ 7,896,863
Wtd. Avg. All-in Cost	1.77%	1.83%
Collateral	$ 15,258,991	$ 12,040,907
Wtd. Avg. All-in Yield	3.41%	3.40%
Net Interest Margin	1.64%	1.57%
1.50% or less [Member]
Schedule Of All In Cost Of Secured Credit Facilities [Line Items]
New Financings	$ 3,065,115	$ 376,085
Total Borrowings	$ 6,288,807	$ 4,192,280
Wtd. Avg. All-in Cost	1.54%	1.59%
Collateral	$ 8,176,251	$ 6,338,626
Wtd. Avg. All-in Yield	3.09%	3.09%
Net Interest Margin	1.55%	1.50%
1.51% to + 1.75% [Member]
Schedule Of All In Cost Of Secured Credit Facilities [Line Items]
New Financings	$ 1,268,796	$ 172,447
Total Borrowings	$ 2,780,867	$ 1,945,692
Wtd. Avg. All-in Cost	1.88%	1.95%
Collateral	$ 3,851,597	$ 2,975,581
Wtd. Avg. All-in Yield	3.40%	3.43%
Net Interest Margin	1.52%	1.48%
1.76% to + 2.00% [Member]
Schedule Of All In Cost Of Secured Credit Facilities [Line Items]
New Financings	$ 479,767	$ 215,056
Total Borrowings	$ 897,258	$ 926,666
Wtd. Avg. All-in Cost	2.08%	2.06%
Collateral	$ 1,253,906	$ 1,212,546
Wtd. Avg. All-in Yield	3.95%	3.83%
Net Interest Margin	1.87%	1.77%
2.01% or more [Member]
Schedule Of All In Cost Of Secured Credit Facilities [Line Items]
New Financings	$ 465,872	$ 134,928
Total Borrowings	$ 1,221,923	$ 832,225
Wtd. Avg. All-in Cost	2.42%	2.49%
Collateral	$ 1,977,237	$ 1,514,154
Wtd. Avg. All-in Yield	4.42%	4.34%
Net Interest Margin	2.00%	1.85%