Fair Value Measurements - Assets and Liabilities, Not at FV (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Assets:
Investments held to maturity	$ 3,446	$ 3,446
Purchased future receivables, net	3,717	9,483
Investment in unconsolidated joint venture	7,169	7,360
Liabilities:
Senior secured notes, net	345,570	345,127
Carrying Amount
Assets:
Loans, held-for-investment	9,743,165	10,622,137
Loans, held for sale	508,946
Servicing rights	103,555	102,837
Total assets	10,355,666	10,724,974
Liabilities:
Secured borrowings	2,198,272	2,102,075
Securitized debt obligations of consolidated VIEs	4,769,057	5,068,453
Senior secured notes, net	345,570	345,127
Guaranteed loan financing	814,784	844,540
Corporate debt, net	766,084	764,908
Total liabilities	8,893,767	9,125,103
Fair Value
Assets:
Loans, held-for-investment	9,585,442	10,380,893
Loans, held for sale	508,946
Servicing rights	116,814	113,715
Total assets	10,211,202	10,494,608
Liabilities:
Secured borrowings	2,198,272	2,102,075
Securitized debt obligations of consolidated VIEs	4,739,186	5,022,057
Senior secured notes, net	319,102	317,239
Guaranteed loan financing	865,630	889,744
Corporate debt, net	739,437	731,104
Total liabilities	$ 8,861,627	$ 9,062,219