Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Operating activities:
Net income	$ 88,505	$ 77,233
Noncash items:
Amortization of investment premiums	40,195	28,351
Depreciation and other amortization	99	107
Equity-based compensation costs	1,098	884
Change in measureable hedge ineffectiveness related to interest rate swap agreements	(147)	(116)
Impairment charge related to real estate held for sale		470
Gain on sales of real estate held for sale	(199)
Net change in receivables, other assets, accounts payable and accrued expenses	(19,418)	(7,367)
Net cash provided by operating activities	110,133	99,562
Investing activities:
Purchases of residential mortgage investments	(2,684,789)	(3,858,053)
Purchased interest receivable related to purchases of residential mortgage investments	(4,382)	(8,290)
Proceeds from sales of real estate held for sale	1,415	523
Principal collections on residential mortgage investments	1,177,686	951,679
Net cash used in investing activities	(1,510,070)	(2,914,141)
Financing activities:
Proceeds from repurchase arrangements and similar borrowings	62,587,261	37,924,609
Principal payments on repurchase arrangements and similar borrowings	(61,210,906)	(35,279,964)
(Increase) decrease in cash collateral receivable from interest rate swap counterparties	(7,253)	1,962
Decrease in cash collateral payable to interest rate swap counterparties		(8,424)
Capital stock transactions	125,548	143,347
Dividends paid	(88,189)	(68,164)
Net cash provided by financing activities	1,406,461	2,713,366
Net change in cash and cash equivalents	6,524	(101,213)
Cash and cash equivalents at beginning of period	426,717	359,590
Cash and cash equivalents at end of period	$ 433,241	$ 258,377