CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash flows from operating activities:
Net income (loss)	$ 344,461	$ 1,267,280	$ 1,961,471
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Amortization of Investment premiums and discounts, net	794,205	664,429	253,683
Amortization of intangibles	2,300	1,600	2,316
Amortization of deferred expenses	3,600	3,150
Amortization of contingent beneficial conversion feature on convertible senior notes	7,550
(Gains) losses on sales of Agency mortgage-backed securities and debentures	(206,846)	(181,791)	(99,128)
Stock option and long-term compensation expense	5,269	4,757	4,514
Unrealized (gains) losses on equity securities	100
Unrealized (gains) losses on interest rate swaps	1,815,107	318,832	(349,521)
Unrealized (gains) losses on interest-only Agency mortgage-backed securities	106,657
Net (gains) losses on trading assets	(21,398)	2,351
(Gain) loss on investment with affiliate, equity method	(98)	(318)	252
Proceeds from repurchase agreements from Broker Dealer	877,734,065	1,268,429,168	301,505,728
Payments on repurchase agreements from Broker Dealer	(878,806,056)	(1,258,941,064)	(291,820,728)
Proceeds from reverse repurchase agreements to Broker Dealer	156,659,365	87,968,002	3,100,827
Payments on reverse repurchase agreements to Broker Dealer	(156,502,577)	(88,479,412)	(3,595,580)
Proceeds from reverse repurchase agreements to Shannon	166,354
Payments on reverse repurchase agreements to Shannon	(177,845)
Proceeds from securities borrowed	27,261,366	2,924,082	152,027
Payments on securities borrowed	(27,973,422)	(3,111,681)	(181,104)
Proceeds from securities loaned	54,126,121	3,231,198	197,100
Payments on securities loaned	(53,539,061)	(3,042,414)	(168,043)
Proceeds from U.S. Treasury Securities	29,168,074	9,331,089
Payments on U.S. Treasury Securities	(28,490,573)	(9,521,134)
Net payments on derivatives	(7,158)	(3,455)
Net change in:
Other assets	(3,258)	3,950	(8,780)
Accrued interest and dividends receivable	(64,362)	(27,125)	(35,574)
Receivable for advisory and service fees	(3,378)	(3,606)	(6,462)
Receivable from Prime Broker			13,613
Accrued interest payable	23,199	26,306	(110,524)
Accounts payable and other liabilities	(1,698)	(1,084)	1,624
Net cash provided by (used in) operating activities	2,420,063	10,863,110	10,817,711
Cash flows from investing activities:
Payments on purchases of Agency mortgage-backed securities and debentures	(69,065,069)	(54,424,951)	(25,911,199)
Proceeds from sales of Agency mortgage-backed securities and debentures	19,337,053	9,262,772	4,029,801
Principal payments on Agency mortgage-backed securities	23,565,709	28,961,203	13,796,269
Proceeds from Agency debentures called	1,124,000	2,132,002	602,000
Payments on purchase of corporate debt	(31,675)	(21,670)
Principal payments on corporate debt	1,375
Net gains (losses) on other derivative securities	13,965
Purchase of investment in affiliate	(57,500)		(157,995)
Purchase of customer relationships	(3,555)
Purchase of equity securities	(3,990)
Proceeds from reverse repurchase agreements		4,291,430	10,355,095
Payments on reverse repurchase agreements		(4,032,426)	(10,051,980)
Earn out payment		(14,113)
Net cash provided by (used in) investing activities	(25,119,687)	(13,845,753)	(7,338,009)
Cash flows from financing activities:
Proceeds from repurchase agreements	273,023,622	224,789,731	327,758,745
Principal payments on repurchase agreements	(253,387,283)	(223,342,427)	(329,520,501)
Proceeds from exercise of stock options	8,953	4,598	4,914
Issuance of Convertible Senior Notes		582,000
Proceeds from direct purchase and dividend reinvestment	455,547	278,784	141,775
Net proceeds from common stock follow-on offerings	5,351,846	1,047,354
Dividends paid	(2,041,489)	(1,599,339)	(1,269,420)
Net cash provided by (used in) financing activities	23,411,196	1,760,701	(2,884,487)
Net increase (decrease) in cash and cash equivalents	711,572	(1,221,942)	595,215
Cash and cash equivalents, beginning of year	282,626	1,504,568	909,353
Cash and cash equivalents, end of year	994,198	282,626	1,504,568
Supplemental disclosure of cash flow information:
Interest received	4,309,690	3,322,228	3,146,933
Dividends received	31,876	30,042	10,149
Fees received	75,827	54,467	42,489
Interest paid (excluding interest paid on interest rate swaps)	455,873	411,608	700,289
Net interest paid on interest rate swaps	876,099	725,418	705,998
Taxes paid	61,045	36,742	42,268
Noncash investing activities:
Receivable for investments sold		151,460	732,134
Payable for investments purchased	4,315,796	4,575,026	4,083,786
Net change in unrealized gains (losses) on available-for-sale securities and interest rate swaps, net of reclassification adjustment	1,844,346	(726,675)	1,639,087
Noncash financing activities:
Dividends declared, not yet paid	552,806	404,220	414,851
Conversion of Series B Cumulative Convertible preferred stock	7,759	23,081	32,928
Contingent beneficial conversion feature on Senior Convertible Notes	$ 60,087