QUARTERLY RESULTS (UNAUDITED) - Summarized Quarterly Results of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended																12 Months Ended
		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Interest income on residential mortgage investments		$ 72,902		$ 67,649		$ 65,202		$ 69,138		$ 64,418		$ 57,073		$ 56,103		$ 54,841		$ 274,891	$ 232,435	$ 212,694
Related interest expense		(59,321)		(54,393)		(48,241)		(45,021)		(40,012)		(36,655)		(33,850)		(28,240)
Net interest income		13,581		13,256		16,961		24,117		24,406		20,418		22,253		26,601		61,993	87,032	97,845
Other interest income (expense)	[1]	(1,284)		(1,560)		(1,595)		(1,483)		(1,702)		(1,544)		(1,662)		(1,738)
Other revenue (expense)		(3,313)	[2]	(3,016)	[2]	(2,378)	[2]	(3,214)	[2]	(117)	[2]	(2,122)	[2]	(3,042)	[2]	(2,162)	[2]	$ (11,921)	$ (7,443)	$ (14,972)
Net income		$ 8,984		$ 8,680		$ 12,988		$ 19,420		$ 22,587		$ 16,752		$ 17,549		$ 22,701
Basic and diluted net income per common share		$ 0.05		$ 0.04		$ 0.09		$ 0.16		$ 0.19		$ 0.13		$ 0.14		$ 0.20		$ 0.34	$ 0.65	$ 0.70

[1] Consists principally of interest on unsecured borrowings, overnight investments and cash collateral receivable with interest rate swap counterparties.

[2] Consists of general and administrative expenses, including compensation-related costs, and miscellaneous other revenue (expense). The fourth quarter of 2017 includes $1.9 million in alternative minimum tax refunds recorded in connection with the enactment of tax reform legislation.