Consolidated Balance Sheets (USD $)	Dec. 31, 2011		Dec. 31, 2010
Assets:
Mortgage securities and similar investments ($11.93 billion and $8.22 billion pledged under repurchase arrangements at December 31, 2011 and 2010, respectively)	$ 12,264,906,000	[1]	$ 8,515,691,000	[1]
Cash collateral receivable from interest rate swap counterparties	48,505,000		35,289,000
Interest rate swap agreements at fair value	617,000		9,597,000
Cash and cash equivalents	426,717,000		359,590,000
Receivables and other assets	100,760,000		76,078,000
Investments in unconsolidated affiliates	3,117,000		3,117,000
Assets, total	12,844,622,000		8,999,362,000
Liabilities:
Repurchase arrangements and similar borrowings	11,352,444,000		7,792,743,000
Cash collateral payable to interest rate swap counterparties			9,024,000
Interest rate swap agreements at fair value	31,348,000		16,337,000
Unsecured borrowings	103,095,000		103,095,000
Common stock dividend payable	38,184,000		27,401,000
Accounts payable and accrued expenses	26,844,000		23,337,000
Liabilities, total	11,551,915,000		7,971,937,000
Stockholders' equity:
Common stock - $0.01 par value; 250,000 shares authorized: 88,287 and 70,259 shares issued and outstanding at December 31, 2011 and December 31, 2010, respectively	883,000		703,000
Paid-in capital	1,257,653,000		1,028,382,000
Accumulated deficit	(354,883,000)		(354,883,000)
Accumulated other comprehensive income	204,540,000		173,900,000
Stockholders' equity attributable to parent, total	1,292,707,000		1,027,425,000
Liabilities and stockholders' equity, total	12,844,622,000		8,999,362,000
$1.60 Cumulative Preferred Stock, Series A [Member]
Stockholders' equity:
Preferred stock-$0.10 par value; 100,000 shares authorized:	2,605,000		2,620,000
$1.26 Cumulative Convertible Preferred Stock, Series B [Member]
Stockholders' equity:
Preferred stock-$0.10 par value; 100,000 shares authorized:	$ 181,909,000		$ 176,703,000

[1] Includes unrealized gains and losses for securities classified as available-for-sale, if applicable, (see NOTE 8).