Mortgage-Backed Securities and other securities - Sales and realized gains (losses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale, Gain (Loss) [Abstract]
Net Gain (Loss)	$ (10,927)	$ 84,271	$ 28,278
Agency CMBS
Debt Securities, Available-for-sale, Gain (Loss) [Abstract]
Proceeds		1,668,149	891,072
Gross Gains		116,463	32,793
Gross Losses		(6,486)	(4,190)
Net Gain (Loss)		109,977	28,603
Agency RMBS
Debt Securities, Available-for-sale, Gain (Loss) [Abstract]
Proceeds		400,948	205,310
Gross Gains		12,552	1,559
Gross Losses		(506)	0
Net Gain (Loss)		12,046	1,559
Non-Agency CMBS
Debt Securities, Available-for-sale, Gain (Loss) [Abstract]
Proceeds	27,488	111,804	40,235
Gross Gains	0	1	317
Gross Losses	(9,266)	(23,624)	(1,624)
Net Gain (Loss)	(9,266)	(23,623)	(1,307)
Non-Agency RMBS
Debt Securities, Available-for-sale, Gain (Loss) [Abstract]
Proceeds		12,658
Gross Gains		0
Gross Losses		(60)
Net Gain (Loss)		(60)
Other securities
Debt Securities, Available-for-sale, Gain (Loss) [Abstract]
Proceeds		35,957
Gross Gains		113
Gross Losses		(6,223)
Net Gain (Loss)		(6,110)
Total mortgage-backed securities and other securities
Debt Securities, Available-for-sale, Gain (Loss) [Abstract]
Proceeds	27,488	2,229,516	1,136,617
Gross Gains	0	129,129	34,669
Gross Losses	(9,266)	(36,899)	(5,814)
Net Gain (Loss)	$ (9,266)	$ 92,230	$ 28,855