General and Administrative Expenses, Loan Acquisition Costs, and Other Expenses - Components of Operating Expenses (Details) - USD ($) $ in Thousands		1 Months Ended		3 Months Ended			12 Months Ended
	Oct. 15, 2019	Dec. 31, 2020	Oct. 31, 2019	Dec. 31, 2020	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Fixed compensation expense							$ 46,689	$ 39,639	$ 24,445
Variable compensation expense							14,116	21,728	14,589
Long-term incentive award expense							12,439	13,402	12,388
Acquisition-related equity compensation expense							4,848	1,010	0
Systems and consulting							11,728	10,746	7,451
Office costs							7,794	6,310	4,705
Accounting and legal							7,928	5,450	5,529
Corporate costs							2,829	2,351	1,955
Other							6,833	8,101	4,236
Total General and Administrative Expenses							115,204	108,737	75,298
Commissions							4,321	3,833	78
Underwriting costs							4,945	4,767	5,140
Transfer and holding costs							1,757	1,335	2,266
Loan acquisition costs							11,023	9,935	7,484
Goodwill impairment expense						$ 89,000	88,675	0	0
Amortization of purchase-related intangible assets							15,925	8,696	177
Contingent consideration expense							200	3,218	0
Other							3,936	1,108	19
Total Other Expenses							108,785	13,022	196
Total General and Administrative Expenses, Loan Acquisition Costs, and Other Expenses							235,012	$ 131,694	$ 82,978
Variable compensation expense							5,000
Settlement in Common Stock
Goodwill [Line Items]
Long-term incentive award expense							10,000
Settlement in Cash
Goodwill [Line Items]
Long-term incentive award expense							2,000
Cash Based Retention Award
Goodwill [Line Items]
Cash based retention awards granted					$ 8,000
Cash based retention awards, term				3 years	3 years
Cash Based Retention Award | Certain Executives and Non-Executive Employees
Goodwill [Line Items]
Cash based retention awards granted					$ 2,000
Long Term Relative TSR Performance Vesting Cash Awards
Goodwill [Line Items]
Cash based retention awards, service period					3 years
Cash-Settled Deferred Stock Units
Goodwill [Line Items]
Cash based retention awards granted		$ 2,000		$ 2,000			$ 2,000
Cash based retention awards, term		4 years
Variable compensation expense		$ 2,000
CoreVest LLC
Goodwill [Line Items]
Acquisition-related equity compensation expense			$ 10,000
Restricted stock awards (in shares)	588,260
Restricted stock awards	$ 10,000		$ 10,000
Contingent consideration performance term	2 years