Consolidated Statements of Income (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Interest income:
Residential mortgage investments	$ 63,463,000	$ 62,890,000	$ 194,983,000	$ 179,167,000
Other	154,000	59,000	480,000	230,000
Interest income	63,617,000	62,949,000	195,463,000	179,397,000
Interest expense:
Repurchase arrangements and similar borrowings	(17,875,000)	(15,744,000)	(48,429,000)	(41,772,000)
Unsecured borrowings	(2,186,000)	(2,186,000)	(6,560,000)	(6,560,000)
Other				(5,000)
Interest expense	(20,061,000)	(17,930,000)	(54,989,000)	(48,337,000)
Net interest income (expense)	43,556,000	45,019,000	140,474,000	131,060,000
Other revenue (expense):
Miscellaneous other revenue (expense)	9,000	(109,000)	(147,000)	(926,000)
Incentive compensation	(781,000)	(1,429,000)	(3,614,000)	(4,149,000)
Salaries and benefits	(1,696,000)	(1,631,000)	(5,205,000)	(5,004,000)
Other general and administrative expense	(1,115,000)	(911,000)	(3,160,000)	(2,939,000)
Operating expenses	(3,583,000)	(4,080,000)	(12,126,000)	(13,018,000)
Income before equity in earnings of unconsolidated affiliates	39,973,000	40,939,000	128,348,000	118,042,000
Equity in earnings of unconsolidated affiliates	64,000	64,000	194,000	194,000
Net income	40,037,000	41,003,000	128,542,000	118,236,000
Net income available to common stockholders:
Net income	40,037,000	41,003,000	128,542,000	118,236,000
Less cash dividends paid on preferred shares	(5,270,000)	(5,105,000)	(15,751,000)	(15,223,000)
Net income (loss) available to common stockholders, basic, total	$ 34,767,000	$ 35,898,000	$ 112,791,000	$ 103,013,000
Net income per common share:
Basic	$ 0.35	$ 0.43	$ 1.20	$ 1.33
Diluted	$ 0.35	$ 0.43	$ 1.20	$ 1.32
Cash dividends declared per share:
Common	$ 0.360	$ 0.440	$ 1.190	$ 1.330
Convertible Preferred Stock [Member] | $1.60 Cumulative Preferred Stock, Series A [Member]
Cash dividends declared per share:
Preferred	$ 0.400	$ 0.400	$ 1.200	$ 1.200
Convertible Preferred Stock [Member] | $1.26 Cumulative Convertible Preferred Stock, Series B [Member]
Cash dividends declared per share:
Preferred	$ 0.315	$ 0.315	$ 0.945	$ 0.945