Valuation (Fair Value Measurement Using Significant Unobservable Inputs) (Details) (Level 3 [Member], USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	$ 638,486,000	$ 756,934,000
Assets, Accreted Discounts/Amortized Premiums	(3,573,000)	4,023,000
Assets, Realized Gain (Loss)	3,976,000	25,480,000
Assets, Change In Net Unrealized Gain/(Loss)	23,000	(11,972,000)
Assets, Purchases	100,888,000	163,958,000
Assets, Sales	(146,400,000)	(244,020,000)
Assets, Transfers into Level 3	23,221,000	0
Assets, Transfers out of Level 3	(102,085,000)	0
Assets, Ending Balance	514,536,000	694,403,000
Liabilities, Begining Balance	(1,013,000)	(1,333,000)
Liabilities, Accreted Discounts/Amortized Premiums	(2,000)	(7,000)
Liabilities, Realized Gain/(Loss)	(19,000)	(19,000)
Liabilities, Change In Net Unrealized Gain/(Loss)	(288,000)	(17,000)
Liabilities Purchases/Payments	88,000	24,000
Liabilities, Sales/Issuance	19,000	19,000
Liabilities, Transfers into Level 3	0	0
Liabilities, Transfers out of Level 3	0	0
Liabilities, Ending Balance	(1,215,000)	(1,333,000)
Change in net unrealized gain (loss) on investments	(3,200,000)	2,300,000
Change in net unrealized gain (loss) in financial derivative assets	(200,000)	(1,200,000)
Change in net unrealized Gain (Loss) on financial derivative liabilities	(300,000)
Change in net unrealized gain (loss) in securitized debt	19,000	(17,000)
Securitized Debt [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Liabilities, Begining Balance	(774,000)	(983,000)
Liabilities, Accreted Discounts/Amortized Premiums	(2,000)	(7,000)
Liabilities, Realized Gain/(Loss)	0	0
Liabilities, Change In Net Unrealized Gain/(Loss)	19,000	(17,000)
Liabilities, Payments	88,000	24,000
Liabilities, Issuances	0	0
Liabilities, Transfers into Level 3	0	0
Liabilities, Transfers out of Level 3	0	0
Liabilities, Ending Balance	(669,000)	(983,000)
Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	626,999,000	740,288,000
Assets, Accreted Discounts/Amortized Premiums	(3,573,000)	4,023,000
Assets, Realized Gain (Loss)	3,575,000	24,290,000
Assets, Change In Net Unrealized Gain/(Loss)	260,000	(10,762,000)
Assets, Purchases	100,866,000	163,919,000
Assets, Sales	(145,754,000)	(242,529,000)
Assets, Transfers into Level 3	23,221,000	0
Assets, Transfers out of Level 3	(102,085,000)	0
Assets, Ending Balance	503,509,000	679,229,000
Investments [Member] | Agency residential mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	31,385,000	40,504,000
Assets, Accreted Discounts/Amortized Premiums	(2,006,000)	(2,289,000)
Assets, Realized Gain (Loss)	471,000	35,000
Assets, Change In Net Unrealized Gain/(Loss)	(96,000)	751,000
Assets, Purchases	1,190,000	2,554,000
Assets, Sales	(4,609,000)	(180,000)
Assets, Transfers into Level 3	0	0
Assets, Transfers out of Level 3	0	0
Assets, Ending Balance	26,335,000	41,375,000
Investments [Member] | Private Label Residential Mortgage-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	274,369,000	580,772,000
Assets, Accreted Discounts/Amortized Premiums	2,388,000	5,385,000
Assets, Realized Gain (Loss)	1,206,000	23,460,000
Assets, Change In Net Unrealized Gain/(Loss)	3,062,000	(12,852,000)
Assets, Purchases	6,633,000	89,585,000
Assets, Sales	(39,423,000)	(196,267,000)
Assets, Transfers into Level 3	23,221,000	0
Assets, Transfers out of Level 3	(102,085,000)	0
Assets, Ending Balance	169,371,000	490,083,000
Investments [Member] | Private Label Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	53,311,000	32,994,000
Assets, Accreted Discounts/Amortized Premiums	1,372,000	205,000
Assets, Realized Gain (Loss)	614,000	872,000
Assets, Change In Net Unrealized Gain/(Loss)	(1,900,000)	1,515,000
Assets, Purchases	15,594,000	37,769,000
Assets, Sales	(16,777,000)	(40,710,000)
Assets, Transfers into Level 3	0	0
Assets, Transfers out of Level 3	0	0
Assets, Ending Balance	52,214,000	32,645,000
Investments [Member] | Commercial Mortgage Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	28,309,000	23,887,000
Assets, Accreted Discounts/Amortized Premiums	539,000	563,000
Assets, Realized Gain (Loss)	0	2,000
Assets, Change In Net Unrealized Gain/(Loss)	17,000	(460,000)
Assets, Purchases	24,291,000	20,023,000
Assets, Sales	(14,238,000)	(10,000)
Assets, Transfers into Level 3	0	0
Assets, Transfers out of Level 3	0	0
Assets, Ending Balance	38,918,000	44,005,000
Investments [Member] | Residential Mortgage Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	27,482,000	24,062,000
Assets, Accreted Discounts/Amortized Premiums	443,000	0
Assets, Realized Gain (Loss)	242,000	18,000
Assets, Change In Net Unrealized Gain/(Loss)	144,000	(260,000)
Assets, Purchases	5,976,000	0
Assets, Sales	(3,442,000)	(254,000)
Assets, Transfers into Level 3	0	0
Assets, Transfers out of Level 3	0	0
Assets, Ending Balance	30,845,000	23,566,000
Investments [Member] | Other asset-backed securities and loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	146,288,000
Assets, Accreted Discounts/Amortized Premiums	(6,340,000)
Assets, Realized Gain (Loss)	772,000
Assets, Change In Net Unrealized Gain/(Loss)	(1,154,000)
Assets, Purchases	26,534,000
Assets, Sales	(42,480,000)
Assets, Transfers into Level 3	0
Assets, Transfers out of Level 3	0
Assets, Ending Balance	123,620,000
Investments [Member] | Corporate Debt [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	42,708,000
Assets, Accreted Discounts/Amortized Premiums	31,000
Assets, Realized Gain (Loss)	186,000
Assets, Change In Net Unrealized Gain/(Loss)	(580,000)
Assets, Purchases	11,605,000
Assets, Sales	(22,114,000)
Assets, Transfers into Level 3	0
Assets, Transfers out of Level 3	0
Assets, Ending Balance	31,836,000
Investments [Member] | Real Estate Owned [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	8,635,000	0
Assets, Accreted Discounts/Amortized Premiums	0	0
Assets, Realized Gain (Loss)	84,000	0
Assets, Change In Net Unrealized Gain/(Loss)	537,000	(4,000)
Assets, Purchases	2,471,000	101,000
Assets, Sales	(2,657,000)	0
Assets, Transfers into Level 3	0	0
Assets, Transfers out of Level 3	0	0
Assets, Ending Balance	9,070,000	97,000
Investments [Member] | Other Asset-backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance		38,069,000
Assets, Accreted Discounts/Amortized Premiums		159,000
Assets, Realized Gain (Loss)		(97,000)
Assets, Change In Net Unrealized Gain/(Loss)		548,000
Assets, Purchases		13,887,000
Assets, Sales		(5,108,000)
Assets, Transfers into Level 3		0
Assets, Transfers out of Level 3		0
Assets, Ending Balance		47,458,000
Investments [Member] | Private Corporate Equity Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	14,512,000
Assets, Accreted Discounts/Amortized Premiums	0
Assets, Realized Gain (Loss)	0
Assets, Change In Net Unrealized Gain/(Loss)	230,000
Assets, Purchases	6,572,000
Assets, Sales	(14,000)
Assets, Transfers into Level 3	0
Assets, Transfers out of Level 3	0
Assets, Ending Balance	21,300,000
Financial Derivatives - Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	11,487,000	16,646,000
Assets, Accreted Discounts/Amortized Premiums	0	0
Assets, Realized Gain (Loss)	401,000	1,190,000
Assets, Change In Net Unrealized Gain/(Loss)	(237,000)	(1,210,000)
Assets, Purchases	22,000	39,000
Assets, Sales	(646,000)	(1,491,000)
Assets, Transfers into Level 3	0	0
Assets, Transfers out of Level 3	0	0
Assets, Ending Balance	11,027,000	15,174,000
Financial Derivatives - Assets [Member] | Credit Default Swaps On Asset Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	11,387,000	16,646,000
Assets, Accreted Discounts/Amortized Premiums	0	0
Assets, Realized Gain (Loss)	401,000	1,190,000
Assets, Change In Net Unrealized Gain/(Loss)	(355,000)	(1,210,000)
Assets, Purchases	22,000	39,000
Assets, Sales	(646,000)	(1,491,000)
Assets, Transfers into Level 3	0	0
Assets, Transfers out of Level 3	0	0
Assets, Ending Balance	10,809,000	15,174,000
Financial Derivatives - Assets [Member] | Total Return Swaps [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	0
Assets, Accreted Discounts/Amortized Premiums	0
Assets, Realized Gain (Loss)	0
Assets, Change In Net Unrealized Gain/(Loss)	118,000
Assets, Purchases	0
Assets, Sales	0
Assets, Transfers into Level 3	0
Assets, Transfers out of Level 3	0
Assets, Ending Balance	118,000
Financial Derivatives - Assets [Member] | Warrant [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	100,000
Assets, Accreted Discounts/Amortized Premiums	0
Assets, Realized Gain (Loss)	0
Assets, Change In Net Unrealized Gain/(Loss)	0
Assets, Purchases	0
Assets, Sales	0
Assets, Transfers into Level 3	0
Assets, Transfers out of Level 3	0
Assets, Ending Balance	100,000
Financial Derivatives - Liabilities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Liabilities, Begining Balance	(239,000)	(350,000)
Liabilities, Accreted Discounts/Amortized Premiums	0	0
Liabilities, Realized Gain/(Loss)	(19,000)	(19,000)
Liabilities, Change In Net Unrealized Gain/(Loss)	(307,000)	0
Liabilities, Purchases	0	0
Liabilities, Sales	19,000	19,000
Liabilities, Transfers into Level 3	0	0
Liabilities, Transfers out of Level 3	0	0
Liabilities, Ending Balance	(546,000)	(350,000)
Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Asset Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Liabilities, Begining Balance	(239,000)	(350,000)
Liabilities, Accreted Discounts/Amortized Premiums	0	0
Liabilities, Realized Gain/(Loss)	(19,000)	(19,000)
Liabilities, Change In Net Unrealized Gain/(Loss)	0	0
Liabilities, Purchases	0	0
Liabilities, Sales	19,000	19,000
Liabilities, Transfers into Level 3	0	0
Liabilities, Transfers out of Level 3	0	0
Liabilities, Ending Balance	(239,000)	(350,000)
Financial Derivatives - Liabilities [Member] | Total Return Swaps [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Liabilities, Begining Balance	0
Liabilities, Accreted Discounts/Amortized Premiums	0
Liabilities, Realized Gain/(Loss)	0
Liabilities, Change In Net Unrealized Gain/(Loss)	(307,000)
Liabilities, Purchases	0
Liabilities, Sales	0
Liabilities, Transfers into Level 3	0
Liabilities, Transfers out of Level 3	0
Liabilities, Ending Balance	$ (307,000)