Fair Value Disclosures (Analysis of Level 3 Assets and Liabilities Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	$ 147,000	$ 73,400	$ 157,800	$ 157,700
Transfers of assets from Level 3 to Level 2	91,800	91,400	114,500	88,100
Transfers of liabilities from Level 3 to Level 2			10,200
Net gains (losses) on Level 3 assets (realized and unrealized)	(5,200)	(48,900)	(85,800)	508,900
Net gains (losses) on Level 3 liabilities (realized and unrealized)	5,400	1,100	(2,800)	(2,900)
Excluded assets from unobservable quantitative information	285,300		285,300		$ 280,600
Excluded liabilities from unobservable quantitative information	1,700		1,700		$ 600
Non-Agency Residential Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3		17,800		21,300
Transfers of assets from Level 3 to Level 2		18,500		15,900
Commercial Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3		3,700	17,200	9,800
Transfers of assets from Level 3 to Level 2		5,200		5,600
Net gains (losses) on Level 3 assets (realized and unrealized)	(1,531)	(510)	(4,606)	(2,053)
Other Asset-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	27,300		38,500	1,400
Transfers of assets from Level 3 to Level 2			17,000
Net gains (losses) on Level 3 assets (realized and unrealized)	(2,247)	870	(2,420)	666
Residential Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	13,700		21,700
Transfers of assets from Level 3 to Level 2	18,300		25,500
Net gains (losses) on Level 3 assets (realized and unrealized)	(2,343)	(3,009)	(7,243)	(6,776)
Municipal securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	34,300		28,700
Net gains (losses) on Level 3 assets (realized and unrealized)	(7,074)		(1,462)
Loans and other receivables [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3		4,100		19,200
Transfers of assets from Level 3 to Level 2	15,800	3,500	19,800	6,100
Net gains (losses) on Level 3 assets (realized and unrealized)	(23,445)	(2,111)	(30,843)	(7,331)
Corporate Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3		5,000		12,200
Net gains (losses) on Level 3 assets (realized and unrealized)	(145)	(5,276)	5,239	(5,425)
CDOs and CLOs [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	23,700	42,800	16,900	16,000
Transfers of assets from Level 3 to Level 2	27,300	39,900	25,300	25,600
Net gains (losses) on Level 3 assets (realized and unrealized)	(4,067)	(12,560)	(24,356)	(28,999)
Corporate Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3				1,600
Transfers of assets from Level 3 to Level 2	20,500	1,900	19,200	11,800
Net gains (losses) on Level 3 assets (realized and unrealized)	(6,492)	3,901	(8,388)	10,247
Investments at Fair Value [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	29,000		26,100	76,200
Transfers of assets from Level 3 to Level 2		21,000		22,700
Net gains (losses) on Level 3 assets (realized and unrealized)	(599)	82,943	46,644	87,254
Other Secured Financings [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of liabilities from Level 3 to Level 2		51,600		51,600
Net gains (losses) on Level 3 liabilities (realized and unrealized)	(200)	0	(276)	0
Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of liabilities from Level 2 to Level 3		2,500
Net gains (losses) on Level 3 liabilities (realized and unrealized)	$ (402)	$ 109	$ 7	$ (102)