General and Administrative Expenses and Other Expenses - Components of Operating Expenses (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
	Oct. 15, 2019	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Line Items]
Fixed compensation expense										$ 39,747	$ 24,445	$ 22,111
Variable compensation expense										25,069	14,589	20,574
Equity compensation expense										13,402	12,388	10,141
Acquisition-related equity compensation expense										1,010	0	0
Systems and consulting										10,746	7,451	7,073
Loan acquisition costs										7,031	7,697	5,022
Office costs										6,310	4,705	4,248
Accounting and legal										5,450	5,529	2,842
Corporate costs										2,351	1,955	1,856
Other										7,556	4,023	3,289
Total General and Administrative Expenses										118,672	82,782	77,156
Amortization of purchase-related intangible assets										8,699	177	0
Contingent consideration expense										3,217	0	0
Other										1,106	19	0
Total Other Expenses										13,022	196	0
Total General and Administrative Expenses and Other Expenses		$ 49,444	$ 29,346	$ 28,707	$ 24,197	$ 19,378	$ 21,561	$ 19,009	$ 23,030	$ 131,694	$ 82,978	77,156
Upfront costs associated with hiring new executive officer												$ 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
Contingent consideration performance term	2 years