CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
U.S. Treasury Securities, pledged assets	$ 2,242,039	$ 352,820	[1]
Agency mortgage-backed securities, pledged assets	105,841,340	90,406,535	[1]
Agency debentures, pledged assets	774,437	567,383	[1]
Receivable for advisory and service fees, from affiliates	16,451	16,245	[1]
Intangible for customer relationships, accumulated amortization	$ 7,177	$ 5,432	[1]
Common stock, par value	$ 0.01	$ 0.01	[1]
Common Stock, shares authorized	1,956,937,500	1,987,987,500	[1]
Common stock, shares issued	974,799,779	970,161,647	[1]
Common stock, shares outstanding	974,799,779	970,161,647	[1]
6.00% Series B Cumulative Convertible Preferred Stock [Member]
Preferred Stock, shares authorized	4,600,000	4,600,000	[1]
Preferred Stock, shares issued	0	1,331,849	[1]
Preferred Stock, shares outstanding	0	1,331,849	[1]
7.875% Series A Cumulative Redeemable Preferred Stock [Member]
Preferred Stock, shares authorized	7,412,500	7,412,500	[1]
Preferred Stock, shares issued	7,412,500	7,412,500	[1]
Preferred Stock, shares outstanding	7,412,500	7,412,500	[1]
7.625% Series C Cumulative Redeemable Preferred Stock [Member]
Preferred Stock, shares authorized	12,650,000	0	[1]
Preferred Stock, shares issued	12,000,000	0	[1]
Preferred Stock, shares outstanding	12,000,000	0	[1]
7.50% Series D Cumulative Redeemable Preferred Stock [Member]
Preferred Stock, shares authorized	18,400,000	0	[1]
Preferred Stock, shares issued	18,400,000	0	[1]
Preferred Stock, shares outstanding	18,400,000	0	[1]

[1] Derived from the audited consolidated financial statements at December 31, 2011.