Consolidated Statements Of Cash Flows (USD $) In Thousands	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Operating activities:
Net income	$ 118,236	$ 93,869
Noncash items:
Amortization of investment premiums	48,023	46,497
Depreciation and other amortization	159	165
Equity-based compensation costs	1,352	1,144
Amounts related to interest rate swap agreements	575	(671)
Impairment charge related to real estate held for sale	470
Increase (decrease) in mortgage securities principal remittance receivable	(30,271)	12,046
Net change in remaining receivables, other assets, accounts payable and accrued expenses	226	2,472
Net cash provided by operating activities	138,770	155,522
Investing activities:
Purchases of mortgage securities and similar investments	(5,263,254)	(2,410,469)
Purchased interest receivable related to purchases of mortgage securities and similar investments	(10,999)	(4,766)
Principal collections on mortgage securities and similar investments	1,547,387	2,511,525
Net cash (used in) provided by investing activities	(3,726,866)	96,290
Financing activities:
Proceeds from repurchase arrangements and similar borrowings	66,614,532	57,170,168
Principal payments on repurchase arrangements and similar borrowings	(63,319,411)	(57,543,035)
Increase in cash collateral receivable from interest rate swap counterparties	(21,839)	(8,253)
Decrease in cash collateral payable to interest rate swap counterparties	(9,024)
Capital stock transactions	197,653	10,233
Dividends paid	(112,238)	(112,911)
Net cash provided by (used in) financing activities	3,349,673	(483,798)
Net change in cash and cash equivalents	(238,423)	(231,986)
Cash and cash equivalents at beginning of period	359,590	409,623
Cash and cash equivalents at end of period	$ 121,167	$ 177,637