QUARTERLY RESULTS (UNAUDITED) - Summarized Quarterly Results of Operations (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
QUARTERLY RESULTS (UNAUDITED) [Abstract]
Interest income on residential mortgage investments (before investment premium amortization)	$ 83,254		$ 85,674		$ 85,214		$ 86,867		$ 90,279		$ 90,614		$ 87,486		$ 84,229
Investment premium amortization	(24,800)		(39,031)		(33,642)		(28,399)		(29,331)		(27,151)		(21,699)		(18,496)		(125,872)	(96,677)	(68,077)
Related interest expense	(15,392)		(15,759)		(16,749)		(18,468)		(20,672)		(17,875)		(16,451)		(14,103)		(66,368)	(69,101)	(57,328)
Net interest income (expense)	43,062		30,884		34,823		40,000		40,276		45,588		49,336		51,630		140,355	178,781	177,298
Other interest income (expense)	(2,066)	[1]	(2,074)	[1]	(2,015)	[1]	(2,010)	[1]	(1,904)	[1]	(1,968)	[1]	(1,946)	[1]	(1,972)	[1]
Other revenue (expense)	(4,023)		(4,108)		(2,914)		(3,072)		(3,288)		(3,583)		(4,055)		(4,488)		(14,117)	(15,414)	(17,353)
Net income	$ 36,973		$ 24,702		$ 29,894		$ 34,918		$ 35,084		$ 40,037		$ 43,335		$ 45,170		$ 126,487	$ 163,626	$ 160,204
Basic net income per common share (in dollars per share)	$ 0.35	[2]	$ 0.23	[2]	$ 0.04	[2]	$ 0.31	[2]	$ 0.31		$ 0.35		$ 0.40		$ 0.45		$ 0.93	$ 1.50	$ 1.76
Diluted net income per common share (in dollars per share)	$ 0.35	[2]	$ 0.23	[2]	$ 0.04	[2]	$ 0.31	[2]	$ 0.31		$ 0.35		$ 0.40		$ 0.44		$ 0.93	$ 1.50	$ 1.75
Redemption preference premiums paid and other one-time effects of the preferred capital transactions (in dollars per share)					$ 0.23

[1] Consists principally of interest on unsecured borrowings and is presented net of earnings of related statutory trusts. These affiliates were dissolved in December 2013.

[2] Includes $0.23 associated with redemption preference premiums paid and other one-time effects of the second quarter’s preferred capital transactions.