Fair Value Disclosures (Analysis of Level 3 Assets and Liabilities Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	$ 98,400	$ 95,200	$ 155,000	$ 94,900
Transfers of assets from Level 3 to Level 2	96,400	59,400	87,000	55,300
Net gains (losses) on Level 3 assets (realized and unrealized)	(109,300)	24,300	557,000	41,800
Net gains (losses) on Level 3 liabilities (realized and unrealized)	4,900	(8,500)	(1,900)	(12,100)
Excluded assets from unobservable quantitative information	178,700		178,700		$ 137,800
Excluded liabilities from unobservable quantitative information	500		500		$ 300
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	30,000	5,500	20,300	20,900
Transfers of assets from Level 3 to Level 2	23,000	35,600	15,100	34,300
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	7,700	14,200	10,200	8,400
Transfers of assets from Level 3 to Level 2	5,500	2,300	3,500	400
Net gains (losses) on Level 3 assets (realized and unrealized)	(789)	(903)	(1,124)	(2,191)
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	2,100	29,900	2,100	25,500
Transfers of assets from Level 3 to Level 2	5,400	1,800		3,500
Net gains (losses) on Level 3 assets (realized and unrealized)	(19)	(314)	(258)	(537)
Loans and Finance 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	1,000	26,300	13,900	14,200
Transfers of assets from Level 3 to Level 2		1,100	5,300	2,600
Net gains (losses) on Level 3 assets (realized and unrealized)	(748)	11,933	(5,795)	3,946
Collateralized Debt Obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	48,000	7,100	27,300	14,300
Transfers of assets from Level 3 to Level 2	54,400	4,700	52,300	3,600
Net gains (losses) on Level 3 assets (realized and unrealized)	(5,120)	4,706	(17,229)	14,169
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	8,200	600	10,400	300
Transfers of liabilities from Level 3 to Level 2				100
Net gains (losses) on Level 3 assets (realized and unrealized)	(532)	5,659	(796)	5,116
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	1,400	11,600	1,600	11,500
Transfers of assets from Level 3 to Level 2	7,000	7,400	10,300	3,600
Net gains (losses) on Level 3 assets (realized and unrealized)	8,030	(178)	7,066	(1,583)
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			69,200
Transfers of assets from Level 3 to Level 2		6,500		7,200
Net gains (losses) on Level 3 assets (realized and unrealized)	3,766	4,155	4,311	27,020
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		11,700		2,800
Transfers of liabilities from Level 3 to Level 2			3,000
Net gains (losses) on Level 3 liabilities (realized and unrealized)	$ (332)	62	$ (277)	754
Net Derivatives, Liabilities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of liabilities from Level 3 to Level 2		$ 3,900
Derivative Financial Instruments Liabilities Net [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of liabilities from Level 3 to Level 2				$ 3,300