Condensed Statement of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Cash Flows From Operating Activities:
Net income	$ 10,976
Adjustments to reconcile net income to net cash provided by operating activities:
Accretion (amortization) of discounts and premiums, investments	286
Net gain on Non-Agency Securities	(2,210)
Changes in operating assets and liabilities:
Decrease in accrued interest receivable	46
Increase in prepaid and other assets	(153)
Increase in derivatives, at fair value	(2,494)
Decrease in accrued interest payable	(108)
Increase in accounts payable and accrued expenses	27
Net cash provided by operating activities	7,419
Cash Flows From Investing Activities:
Purchases of Non-Agency Securities	(9,757)
Principal repayments of Agency Securities	17,188
Principal repayments of Non-Agency Securities	4,875
Increase in cash collateral	4,082
Net cash provided by investing activities	16,388
Cash Flows From Financing Activities:
Proceeds from repurchase agreements	1,609,523
Principal repayments on repurchase agreements	(1,636,411)
Common dividends paid	(5,175)
Net cash used in financing activities	(32,063)
Net decrease in cash	(8,256)
Cash - beginning of period	36,316
Cash - end of period	28,060
Supplemental Disclosure:
Cash paid during the period for interest	1,808
Non-Cash Investing and Financing Activities:
Unrealized loss on investment on available for sale securities	(15,840)
Angency Securities [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Accretion (amortization) of discounts and premiums, investments	1,049
Non-Agency Securities [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Accretion (amortization) of discounts and premiums, investments	$ 286