Variable interest entities and securitization activities - Securitized Debt Obligations (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Variable interest entities
Current Principal Balance	$ 1,676,150	$ 1,470,532
Carrying value	1,465,539	905,367
Consolidated VIEs
Variable interest entities
Current Principal Balance	1,496,126	926,761
Carrying value	$ 1,465,539	$ 905,367
Weighted Average Rate	3.90%	4.00%
Waterfall Victoria Mortgage Trust 2011-SBC2
Variable interest entities
Current Principal Balance	$ 8,368	$ 12,226
Carrying value	$ 8,368	$ 12,226
Weighted Average Rate	5.50%	5.40%
ReadyCap Lending Small Business Trust 2015-1
Variable interest entities
Current Principal Balance		$ 3,397
Carrying value		$ 1,180
Weighted Average Rate		3.40%
Sutherland Commercial Mortgage Trust 2017-SBC6
Variable interest entities
Current Principal Balance	$ 48,706	$ 69,764
Carrying value	$ 47,800	$ 68,574
Weighted Average Rate	3.40%	3.30%
Sutherland Commercial Mortgage Trust 2018-SBC7
Variable interest entities
Current Principal Balance	$ 158,891	$ 205,451
Carrying value	$ 156,651	$ 202,491
Weighted Average Rate	4.70%	4.70%
Sutherland Commercial Mortgage Trust 2019-SBC8
Variable interest entities
Current Principal Balance	$ 231,121
Carrying value	$ 228,373
Weighted Average Rate	2.90%
ReadyCap Commercial Mortgage Trust 2014-1
Variable interest entities
Current Principal Balance	$ 24,857	$ 36,108
Carrying value	$ 24,863	$ 36,129
Weighted Average Rate	5.60%	4.50%
ReadyCap Commercial Mortgage Trust 2015-2
Variable interest entities
Current Principal Balance	$ 83,138	$ 110,497
Carrying value	$ 80,139	$ 106,755
Weighted Average Rate	4.40%	4.20%
ReadyCap Commercial Mortgage Trust 2016-3
Variable interest entities
Current Principal Balance	$ 39,211	$ 63,945
Carrying value	$ 37,616	$ 62,053
Weighted Average Rate	4.20%	3.70%
ReadyCap Commercial Mortgage Trust 2018-4
Variable interest entities
Current Principal Balance	$ 135,693	$ 144,701
Carrying value	$ 131,799	$ 140,314
Weighted Average Rate	3.90%	3.90%
ReadyCap Commercial Mortgage Trust 2019-5
Variable interest entities
Current Principal Balance	$ 346,882
Carrying value	$ 336,516
Weighted Average Rate	4.10%
Ready Capital Mortgage Financing 2017-FL1
Variable interest entities
Current Principal Balance		$ 63,615
Carrying value		$ 61,902
Weighted Average Rate		3.70%
Ready Capital Mortgage Financing 2018-FL2
Variable interest entities
Current Principal Balance	$ 142,018	$ 217,057
Carrying value	$ 140,128	$ 213,743
Weighted Average Rate	3.80%	3.40%
Ready Capital Mortgage Financing 2019-FL3
Variable interest entities
Current Principal Balance	$ 267,904
Carrying value	$ 263,739
Weighted Average Rate	3.80%
Bear Stearns Commercial Mortgage 2005-TOP20
Variable interest entities
Current Principal Balance	$ 9,337
Carrying value	$ 9,547
Weighted Average Rate	5.70%