Fair Value Measurements - Assets and Liabilities, Not at FV (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets:
Purchased future receivables, net	$ 27,190	$ 43,265
Liabilities:
Senior secured notes, net	179,481	179,289
Carrying Amount
Assets:
Loans, held-for-investment	4,030,683	4,033,972
Purchased future receivables, net	27,190	43,265
Servicing rights	34,116	30,795
Total assets	4,091,989	4,108,032
Liabilities:
Secured borrowings	1,253,895	1,189,392
Securitized debt obligations of consolidated VIEs	2,140,009	1,815,154
Senior secured notes, net	179,481	179,289
Guaranteed loan financing	436,532	485,461
Convertible note, net	111,581	111,040
Corporate debt, net	150,387	149,986
Total liabilities	4,271,885	3,930,322
Carrying Amount | Level 3 inputs
Assets:
Due from servicers and accrued interest	13,000	20,700
Receivable from third parties	300	1,200
Liabilities:
Payable to related parties and accrued interest payable	25,700	20,000
Fair Value | Level 3 inputs
Assets:
Loans, held-for-investment	4,065,820	4,147,831
Purchased future receivables, net	27,190	43,265
Servicing rights	38,407	34,723
Total assets	4,131,417	4,225,819
Liabilities:
Secured borrowings	1,253,895	1,189,392
Securitized debt obligations of consolidated VIEs	2,158,456	1,859,047
Senior secured notes, net	186,738	190,923
Guaranteed loan financing	462,852	515,182
Convertible note, net	79,537	116,654
Corporate debt, net	124,302	161,098
Total liabilities	$ 4,265,780	$ 4,032,296