REAL ESTATE AND OTHER SECURITIES - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Provision (reversal) for credit losses on securities	$ 13,404	$ 25,174	$ 30,017
Agency RMBS
Debt Securities, Available-for-sale [Line Items]
Face amount of securities sold		5,100,000
Face amount of securities purchased, unsettled		900,000
Sale price of securities sold		5,200,000
Purchase of real estate securities, unsettled		$ 900,000