Interest income and interest expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Interest income
Total loans	$ 295,622	$ 243,648	$ 218,267
Total loans, held for sale, at fair value	14,991	8,891	5,553
Total Paycheck Protection Program loans	79,201
Mortgage backed securities, at fair value	13,682	6,097	6,096
Total interest income	403,496	258,636	229,916
Interest expense
Secured borrowings	(65,692)	(45,430)	(49,009)
Paycheck Protection Program Liquidity Facility borrowings	(7,140)
Securitized debt obligations of consolidated VIEs	(82,249)	(78,029)	(69,152)
Guaranteed loan financing	(13,900)	(18,399)	(5,125)
Senior secured note	(15,472)	(13,870)	(13,920)
Convertible note	(8,752)	(8,752)	(8,752)
Corporate debt	(20,356)	(11,001)	(5,922)
Total interest expense	(213,561)	(175,481)	(151,880)
Net interest income before provision for loan losses	189,935	83,155	78,036
Acquired SBA 7(a) loans
Interest income
Total loans	15,906	18,251	20,687
Acquired loans
Interest income
Total loans	56,156	57,471	63,879
Total loans, held for sale, at fair value	1,080	166	217
Originated Transitional loans
Interest income
Total loans	151,803	88,271	69,217
Originated SBC loans, at fair value
Interest income
Total loans	886	1,938	1,383
Originated SBC loans
Interest income
Total loans	49,099	57,134	51,617
Originated SBA 7(a) loans
Interest income
Total loans	21,634	20,434	11,409
Paycheck Protection Program Loans
Interest income
Total Paycheck Protection Program loans	78,932
Paycheck Protection Program loans, at fair value
Interest income
Total Paycheck Protection Program loans	269
Originated Residential Agency loans
Interest income
Total loans	138	149	75
Total loans, held for sale, at fair value	11,250	7,532	4,328
Originated Freddie Mac loans
Interest income
Total loans, held for sale, at fair value	$ 2,661	$ 1,193	$ 1,008