Segment Reporting - Schedule of Performance Based Segment Reporting Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Revenue
Interest and related income	$ 103,876	$ 105,984	$ 314,326	$ 340,786
Less: interest and related expense	48,070	39,740	151,188	129,081
Net interest income	55,806	66,244	163,138	211,705
Revenue from real estate owned	8,550		15,620
Total revenue	64,356	66,244	178,758	211,705
Management fees - affiliate	9,789	9,844	29,152	29,111
Incentive fees - affiliate		1,141		7,579
Equity compensation	(186)	2,451	(376)	7,354
General and administrative expenses	1,330	1,169	5,393	4,162
Expenses from real estate owned	9,888		21,912
Total expenses	20,821	14,605	56,081	48,206
Gain on foreclosure of real estate owned			1,430
Other income			5,855
Reversal of current expected credit loss reserve	9,306		17,413
Income before income taxes	52,841		147,375
Income tax benefit			6,025
Realized loss on sale of investments		(202)		(202)
Segment income	52,841	51,437	153,400	163,297
Total Assets as of September 30, 2021	7,352,273	6,952,543	7,352,273	6,952,543	$ 6,952,543
Loan
Revenue
Interest and related income	103,876	105,984	314,326	340,786
Less: interest and related expense	45,429	39,740	138,186	129,081
Net interest income	58,447	66,244	176,140	211,705
Total revenue	58,447	66,244	176,140	211,705
Reversal of current expected credit loss reserve	9,306		17,413
Income before income taxes	67,753		193,553
Realized loss on sale of investments		(202)		(202)
Segment income	67,753	66,042	193,553	211,503
Total Assets as of September 30, 2021	6,905,196	6,952,543	6,905,196	6,952,543
Corporate and Other
Revenue
Less: interest and related expense	2,641		13,002
Net interest income	(2,641)		(13,002)
Revenue from real estate owned	8,550		15,620
Total revenue	5,909		2,618
Management fees - affiliate	9,789	9,844	29,152	29,111
Incentive fees - affiliate		1,141		7,579
Equity compensation	(186)	2,451	(376)	7,354
General and administrative expenses	1,330	1,169	5,393	4,162
Expenses from real estate owned	9,888		21,912
Total expenses	20,821	14,605	56,081	48,206
Gain on foreclosure of real estate owned			1,430
Other income			5,855
Income before income taxes	(14,912)		(46,178)
Income tax benefit			6,025
Segment income	(14,912)	$ (14,605)	(40,153)	$ (48,206)
Total Assets as of September 30, 2021	$ 447,077		$ 447,077