CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
U.S. Treasury Securities, pledged assets	$ 752,076	$ 352,820
Agency mortgage-backed securities, pledged assets	107,466,084	90,406,535
Agency debentures, pledged assets	981,727	567,383
Receivable for advisory and service fees, from affiliates	14,077	16,245
Intangible for customer relationships, accumulated amortization	$ 5,779	$ 5,432
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	1,956,937,500	1,987,987,500
Common stock, shares issued	947,213,204	970,161,647
Common stock, shares outstanding	947,213,204	970,161,647
6.00% Series B Cumulative Convertible Preferred Stock [Member]
Preferred Stock, shares authorized	4,600,000	4,600,000
Preferred Stock, shares issued	0	1,331,849
Preferred Stock, shares outstanding	0	1,331,849
7.875% Series A Cumulative Redeemable Preferred Stock [Member]
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 [Member]
Preferred Stock, shares authorized	12,650,000	0
Preferred Stock, shares issued	12,000,000	0
Preferred Stock, shares outstanding	12,000,000	0
7.50% Series D Cumulative Redeemable Preferred Stock [Member]
Preferred Stock, shares authorized	18,400,000	0
Preferred Stock, shares issued	18,400,000	0
Preferred Stock, shares outstanding	18,400,000	0