CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Cash pledged as collateral	$ 1,584,701,000	$ 371,790,000
U.S. Treasury securities, pledged assets	0	1,113,027,000
Agency mortgage-backed securities, pledged assets	74,006,480,000	63,897,873,000
Agency debentures, pledged assets	1,368,350,000	2,931,261,000
Receivable for investment advisory income, from affiliates	10,402,000	6,839,000
Common Stock, par value	$ 0.01	$ 0.01
Common Stock, shares authorized	1,956,937,500	1,956,937,500
Common Stock, shares issued	947,643,079	947,432,862
Common Stock, shares outstanding	947,643,079	947,432,862
Senior Secured mortgages of Consolidated VIE	1,518,165,000	1,583,969,000
Senior Securitized Mortgages
Senior Secured mortgages of Consolidated VIE	$ 398,600,000
7.875% Series A Cumulative Redeemable Preferred Stock
Preferred Stock, shares authorized	7,412,500	7,412,500
Preferred Stock, shares issued	7,412,500	7,412,500
Preferred Stock, shares outstanding	7,412,500	7,412,500
7.625% Series C Cumulative Redeemable Preferred Stock
Preferred Stock, shares authorized	12,650,000	12,650,000
Preferred Stock, shares issued	12,000,000	12,000,000
Preferred Stock, shares outstanding	12,000,000	12,000,000
7.50% Series D Cumulative Redeemable Preferred Stock
Preferred Stock, shares authorized	18,400,000	18,400,000
Preferred Stock, shares issued	18,400,000	18,400,000
Preferred Stock, shares outstanding	18,400,000	18,400,000