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	$ 291,933	$ 22,390	$ 63,846
Adjustments to reconcile net income to net cash used in operating activities:
Purchase of investment securities	(7,093,540)	(6,612,956)	(1,370,711)
Premium paid on interest rate caps		(18,595)
Proceeds from disposition of investment securities	2,769,867	1,587,025	51,635
Proceeds from paydowns of investment securities	1,406,114	540,531	192,527
Amortization of share based compensation	5,263	1,459	985
Amortization of premiums and discounts on investment securities	43,895	8,885	3,321
Amortization of premiums on interest rate cap contracts	3,838	1,035
Net realized (gain) loss on investments	(35,756)	(6,115)	48
Net unrealized (appreciation) depreciation on swap and cap contracts	100,012	(16,573)	(8,710)
Net unrealized (appreciation) depreciation on investments	225,660	(4,832)	39,561
Change in assets and liabilities:
Receivable for securities sold	(5,550)	2,725	(1,840)
Interest receivable	(11,632)	(9,296)	(3,058)
Other assets	(661)	(117)	(24)
Payable for securities purchased	(1,771,099)	2,004,562	229,839
Accrued interest payable	6,205	6,025	1,060
Related party management fee payable	(800)	443	137
Accrued expenses and other liabilities	675	342	(225)
Net cash used in operating activities	(4,516,896)	(2,483,398)	(880,731)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from repurchase agreements	43,998,829	16,389,071	9,135,440
Repayments of repurchase agreements	(39,561,858)	(14,317,936)	(8,350,218)
Proceeds from issuance of common shares	275,884	489,740	107,741
Offering costs paid		(789)	(1,921)
Distributions paid	(185,961)	(77,068)	(15,577)
Net cash provided by financing activities	4,526,894	2,483,018	875,465
Net increase (decrease) in cash and cash equivalents	9,998	(380)	(5,266)
CASH AND CASH EQUIVALENTS-Beginning of period	1,510	1,890	7,156
CASH AND CASH EQUIVALENTS-End of period	11,508	1,510	1,890
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Interest paid	70,691	19,728	13,665
SUPPLEMENTAL DISCLOSURES OF NONCASH FLOW INFORMATION:
Distributions declared, not yet paid			10,316
Change in accrued offering costs			(511)
Reinvestment of distributions	$ 14	$ 9