Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Operating activities
Net income	$ 137,978	$ 158,448
Adjustments to reconcile net income to net cash provided by operating activities:
Net amortization of premium related to mortgage-backed securities	92,058	65,475
Amortization related to interest rate swap agreements	163	184
Share based compensation expense	1,256	854
Hedge ineffectiveness	(96)	338
Net gain on sale of mortgage-backed securities	(11,302)	(14,710)
Net gain on sale of futures contracts	(5,536)
Changes in operating assets and liabilities:
Decrease (increase) in accrued interest receivable	3,156	(10,831)
Increase in other assets	(730)	(578)
Decrease in accrued interest payable	(2,819)	(203)
Increase (decrease) in accounts payable and other liabilities	1,122	(379)
Net cash provided by operating activities	215,250	198,598
Investing activities
Purchases of mortgage-backed securities	(6,029,805)	(8,959,135)
Principal repayments of mortgage-backed securities	3,180,421	1,938,005
Sale of mortgage-backed securities	2,361,380	2,383,298
Net cash used in investing activities	(488,004)	(4,637,832)
Financing activities
Issuance of common stock, net of cost of issuance		570,589
Cash dividends paid	(149,317)	(139,030)
Increase (decrease) in restricted cash on swap arrangements	131,811	(41,164)
Proceeds from repurchase agreements	126,103,804	102,306,555
Principal repayments on repurchase agreements	(125,892,981)	(98,316,070)
Net cash provided by financing activities	193,317	4,380,880
Net decrease in cash and cash equivalents	(79,437)	(58,354)
Cash and cash equivalents, beginning of period	168,424	347,045
Cash and cash equivalents, end of period	88,987	288,691
Supplemental disclosure of cash flow information
Cash paid during the period for interest	108,123	87,481
Supplemental schedule of non-cash investing activities
Obligation to brokers for purchase of unsettled mortgage-backed securities	1,042,436	2,160,647
Receivable for securities sold	7,251
Preferred Stock
Supplemental schedule of non-cash financing activities
Dividends declared, not yet paid	5,480
Common Stock Amount
Supplemental schedule of non-cash financing activities
Dividends declared, not yet paid	$ 69,181	$ 88,267