Valuation (Fair Value Measurement Using Significant Unobservable Inputs) (Details) (Level 3 [Member], USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	$ 694,403,000	$ 627,575,000	$ 756,934,000	$ 599,914,000
Assets, Accreted Discounts/Amortized Premiums	3,014,000	5,331,000	7,037,000	11,117,000
Assets, Realized Gain (Loss)	12,574,000	4,984,000	38,056,000	22,388,000
Assets, Change In Net Unrealized Gain/(Loss)	2,273,000	(7,125,000)	(9,700,000)	14,829,000
Assets, Purchases	141,089,000	259,987,000	305,047,000	367,223,000
Assets, Sales	(145,260,000)	(76,402,000)	(389,281,000)	(201,121,000)
Assets, Transfers In and/or Out of Level 3	0	0	0	0
Assets, Ending Balance	708,093,000	814,350,000	708,093,000	814,350,000
Liabilities, Begining Balance	(1,333,000)	(1,207,000)	(1,333,000)	(1,336,000)
Liabilities, Accreted Discounts/Amortized Premiums	(5,000)	(11,000)	(12,000)	(20,000)
Liabilities, Realized Gain/(Loss)	(20,000)	(29,000)	(39,000)	(57,000)
Liabilities, Change In Net Unrealized Gain/(Loss)	1,000	(603,000)	(16,000)	(535,000)
Liabilities Purchases/Payments	62,000	111,000	86,000	182,000
Liabilities, Sales/Issuance	20,000	30,000	39,000	57,000
Liabilities, Transfers In and/or Out of Level 3	0	0	0	0
Liabilities, Ending Balance	(1,275,000)	(1,709,000)	(1,275,000)	(1,709,000)
Change in net unrealized gain (loss) on investments	6,000,000	(5,000,000)	6,200,000	21,500,000
Change in net unrealized gain (loss) in financial derivative assets	600,000	1,700,000	(1,500,000)	(9,100,000)
Change in net unrealized Gain (Loss) on financial derivative liabilities		(1,100,000)		(1,100,000)
Change in net unrealized gain (loss) in securitized debt	1,000	63,000	(16,000)	5,000
Securitized Debt [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Liabilities, Begining Balance	(983,000)	(1,205,000)	(983,000)	(1,335,000)
Liabilities, Accreted Discounts/Amortized Premiums	(5,000)	(11,000)	(12,000)	(20,000)
Liabilities, Realized Gain/(Loss)	0	0	0	0
Liabilities, Change In Net Unrealized Gain/(Loss)	1,000	(63,000)	(16,000)	5,000
Liabilities, Payments	62,000	111,000	86,000	182,000
Liabilities, Issuances	0	0	0	0
Liabilities, Transfers In and/or Out of Level 3	0	0	0	0
Liabilities, Ending Balance	(925,000)	(1,168,000)	(925,000)	(1,168,000)
Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	679,229,000	601,177,000	740,288,000	563,883,000
Assets, Accreted Discounts/Amortized Premiums	3,014,000	5,331,000	7,037,000	11,117,000
Assets, Realized Gain (Loss)	13,041,000	5,526,000	37,332,000	19,679,000
Assets, Change In Net Unrealized Gain/(Loss)	1,687,000	(8,232,000)	(9,075,000)	19,321,000
Assets, Purchases	140,672,000	259,945,000	304,591,000	367,132,000
Assets, Sales	(143,712,000)	(70,531,000)	(386,242,000)	(187,916,000)
Assets, Transfers In and/or Out of Level 3	0	0	0	0
Assets, Ending Balance	693,931,000	793,216,000	693,931,000	793,216,000
Investments [Member] | Agency residential mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	41,375,000	16,228,000	40,504,000	6,644,000
Assets, Accreted Discounts/Amortized Premiums	(2,045,000)	(1,132,000)	(4,334,000)	(2,003,000)
Assets, Realized Gain (Loss)	135,000	0	170,000	0
Assets, Change In Net Unrealized Gain/(Loss)	(728,000)	68,000	23,000	306,000
Assets, Purchases	0	12,233,000	2,554,000	22,450,000
Assets, Sales	(2,497,000)	0	(2,677,000)	0
Assets, Transfers In and/or Out of Level 3	0	0	0	0
Assets, Ending Balance	36,240,000	27,397,000	36,240,000	27,397,000
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	490,083,000	557,820,000	580,772,000	528,366,000
Assets, Accreted Discounts/Amortized Premiums	5,203,000	6,471,000	10,589,000	13,112,000
Assets, Realized Gain (Loss)	7,718,000	4,189,000	31,178,000	19,790,000
Assets, Change In Net Unrealized Gain/(Loss)	3,516,000	(6,636,000)	(9,336,000)	17,383,000
Assets, Purchases	64,639,000	184,029,000	154,223,000	256,862,000
Assets, Sales	(85,257,000)	(51,363,000)	(281,524,000)	(141,003,000)
Assets, Transfers In and/or Out of Level 3	0	0	0	0
Assets, Ending Balance	485,902,000	694,510,000	485,902,000	694,510,000
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	32,645,000	5,778,000	32,994,000	19,327,000
Assets, Accreted Discounts/Amortized Premiums	147,000	41,000	352,000	98,000
Assets, Realized Gain (Loss)	3,518,000	324,000	4,391,000	(1,124,000)
Assets, Change In Net Unrealized Gain/(Loss)	(1,979,000)	(771,000)	(464,000)	2,473,000
Assets, Purchases	28,400,000	24,826,000	66,169,000	37,168,000
Assets, Sales	(34,684,000)	(6,292,000)	(75,395,000)	(34,036,000)
Assets, Transfers In and/or Out of Level 3	0	0	0	0
Assets, Ending Balance	28,047,000	23,906,000	28,047,000	23,906,000
Investments [Member] | Commercial Mortgage Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	44,005,000	9,713,000	23,887,000	9,546,000
Assets, Accreted Discounts/Amortized Premiums	521,000	19,000	1,084,000	27,000
Assets, Realized Gain (Loss)	871,000	482,000	872,000	482,000
Assets, Change In Net Unrealized Gain/(Loss)	169,000	(73,000)	(291,000)	86,000
Assets, Purchases	3,980,000	2,550,000	24,004,000	2,551,000
Assets, Sales	(12,131,000)	(5,128,000)	(12,141,000)	(5,129,000)
Assets, Transfers In and/or Out of Level 3	0	0	0	0
Assets, Ending Balance	37,415,000	7,563,000	37,415,000	7,563,000
Investments [Member] | Residential Mortgage Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	23,566,000		24,062,000
Assets, Accreted Discounts/Amortized Premiums	0		0
Assets, Realized Gain (Loss)	359,000		377,000
Assets, Change In Net Unrealized Gain/(Loss)	1,214,000		954,000
Assets, Purchases	1,695,000		1,695,000
Assets, Sales	(3,463,000)		(3,717,000)
Assets, Transfers In and/or Out of Level 3	0		0
Assets, Ending Balance	23,371,000		23,371,000
Investments [Member] | Other Asset-backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	47,458,000	11,638,000	38,069,000	0
Assets, Accreted Discounts/Amortized Premiums	(812,000)	(68,000)	(654,000)	(117,000)
Assets, Realized Gain (Loss)	450,000	531,000	354,000	531,000
Assets, Change In Net Unrealized Gain/(Loss)	(492,000)	(820,000)	56,000	(927,000)
Assets, Purchases	40,300,000	36,307,000	54,187,000	48,101,000
Assets, Sales	(5,589,000)	(7,748,000)	(10,697,000)	(7,748,000)
Assets, Transfers In and/or Out of Level 3	0	0	0	0
Assets, Ending Balance	81,315,000	39,840,000	81,315,000	39,840,000
Investments [Member] | Residential Real Estate [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	97,000		0
Assets, Accreted Discounts/Amortized Premiums	0		0
Assets, Realized Gain (Loss)	(10,000)		(10,000)
Assets, Change In Net Unrealized Gain/(Loss)	(13,000)		(17,000)
Assets, Purchases	1,658,000		1,759,000
Assets, Sales	(91,000)		(91,000)
Assets, Transfers In and/or Out of Level 3	0		0
Assets, Ending Balance	1,641,000		1,641,000
Financial Derivatives - Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	15,174,000	26,398,000	16,646,000	36,031,000
Assets, Accreted Discounts/Amortized Premiums	0	0	0	0
Assets, Realized Gain (Loss)	(467,000)	(542,000)	724,000	2,709,000
Assets, Change In Net Unrealized Gain/(Loss)	586,000	1,107,000	(625,000)	(4,492,000)
Assets, Purchases	417,000	42,000	456,000	91,000
Assets, Sales	(1,548,000)	(5,871,000)	(3,039,000)	(13,205,000)
Assets, Transfers In and/or Out of Level 3	0	0	0	0
Assets, Ending Balance	14,162,000	21,134,000	14,162,000	21,134,000
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	15,174,000	26,398,000	16,646,000	36,031,000
Assets, Accreted Discounts/Amortized Premiums	0	0	0	0
Assets, Realized Gain (Loss)	(467,000)	(542,000)	724,000	2,709,000
Assets, Change In Net Unrealized Gain/(Loss)	586,000	1,107,000	(625,000)	(4,492,000)
Assets, Purchases	417,000	42,000	456,000	91,000
Assets, Sales	(1,548,000)	(5,871,000)	(3,039,000)	(13,205,000)
Assets, Transfers In and/or Out of Level 3	0	0	0	0
Assets, Ending Balance	14,162,000	21,134,000	14,162,000	21,134,000
Financial Derivatives - Liabilities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Liabilities, Begining Balance	(350,000)	(2,000)	(350,000)	(1,000)
Liabilities, Accreted Discounts/Amortized Premiums	0	0	0	0
Liabilities, Realized Gain/(Loss)	(20,000)	(29,000)	(39,000)	(57,000)
Liabilities, Change In Net Unrealized Gain/(Loss)	0	(540,000)	0	(540,000)
Liabilities, Purchases	0	0	0	0
Liabilities, Sales	20,000	30,000	39,000	57,000
Liabilities, Transfers In and/or Out of Level 3	0	0	0	0
Liabilities, Ending Balance	(350,000)	(541,000)	(350,000)	(541,000)
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	(350,000)	(2,000)	(350,000)	(1,000)
Liabilities, Accreted Discounts/Amortized Premiums	0	0	0	0
Liabilities, Realized Gain/(Loss)	(20,000)	(29,000)	(39,000)	(57,000)
Liabilities, Change In Net Unrealized Gain/(Loss)	0	(540,000)	0	(540,000)
Liabilities, Purchases	0	0	0	0
Liabilities, Sales	20,000	30,000	39,000	57,000
Liabilities, Transfers In and/or Out of Level 3	0	0	0	0
Liabilities, Ending Balance	$ (350,000)	$ (541,000)	$ (350,000)	$ (541,000)