Interest income and interest expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Interest income
Total loans	$ 56,558	$ 41,959	$ 156,997	$ 116,281
Total loans, held for sale, at fair value	1,625	1,287	3,976	4,184
Mortgage backed securities, at fair value	1,540	1,041	4,537	2,830
Total interest income	59,723	44,287	165,510	123,295
Interest expense
Secured borrowings	(13,360)	(9,269)	(34,809)	(25,239)
Securitized debt obligations of consolidated VIEs	(17,978)	(9,988)	(51,516)	(25,478)
Guaranteed loan financing	(645)	(3,011)	(3,873)	(8,781)
Senior secured note	(3,478)	(3,489)	(10,444)	(10,215)
Convertible note	(2,188)	(2,187)	(6,564)	(6,560)
Corporate debt	(1,741)	(981)	(3,713)	(1,723)
Total interest expense	(39,390)	(28,925)	(110,919)	(77,996)
Net interest income before provision for loan losses	20,333	15,362	54,591	45,299
Acquired SBA 7(a) loans
Interest income
Total loans	4,609	8,692	16,078	24,532
Acquired loans
Interest income
Total loans	16,247	11,799	44,289	33,966
Total loans, held for sale, at fair value	50	28	123	118
Originated Transitional loans
Interest income
Total loans	20,157	13,306	51,398	32,627
Originated SBC loans, at fair value
Interest income
Total loans	331	767	1,052	3,292
Originated SBC loans
Interest income
Total loans	10,499	6,374	34,679	18,946
Originated SBA 7(a) loans
Interest income
Total loans	2,626	1,006	7,390	2,879
Acquired Transitional loans
Interest income
Total loans	2,059		2,059
Originated Residential Agency loans
Interest income
Total loans	30	15	52	39
Total loans, held for sale, at fair value	1,224	956	3,047	2,820
Originated Freddie Mac loans
Interest income
Total loans, held for sale, at fair value	$ 351	$ 303	$ 806	$ 1,246