Valuation (Fair Value Measurement Using Significant Unobservable Inputs) (Details) - Level 3 [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	$ 523,837		$ 493,541		$ 638,486
Assets, Accreted Discounts/Amortized Premiums	(26,697)		(16,102)		(20,675)
Assets, Realized Gain (Loss)	4,999		(1,827)		20,808
Assets, Change In Net Unrealized Gain/(Loss)	24,585		(1,998)		(29,552)
Assets, Purchases	638,520		487,837		430,683
Assets, Sales	(453,628)		(433,484)		(504,371)
Assets, Transfers into Level 3	14,021		10,041		6,687
Assets, Transfers out of Level 3	(64,049)		(14,171)		(48,525)
Assets, Ending Balance	661,588		523,837		493,541
Liabilities, Begining Balance	(505)		(6,159)		(1,013)
Liabilities, Accreted Discounts/Amortized Premiums	0		(1)		(17)
Liabilities, Realized Gain/(Loss)	(1,425)		(7,495)		2,611
Liabilities, Change In Net Unrealized Gain/(Loss)	1,188		4,977		(5,201)
Liabilities Purchases/Payments	1,308		8,853		2,149
Liabilities, Sales/Issuance	(125,671)		(680)		(4,688)
Liabilities, Transfers into Level 3	0		0		0
Liabilities, Transfers out of Level 3	0		0		0
Liabilities, Ending Balance	(125,105)		(505)		(6,159)
Other secured borrowings [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)	0
Liabilities, Payments	0
Liabilities, Issuances	(125,105)
Liabilities, Transfers into Level 3	0
Liabilities, Transfers out of Level 3	0
Liabilities, Ending Balance	(125,105)		0
Securitized debt [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Liabilities, Begining Balance			0		(774)
Liabilities, Accreted Discounts/Amortized Premiums					(15)
Liabilities, Realized Gain/(Loss)					0
Liabilities, Change In Net Unrealized Gain/(Loss)					26
Liabilities, Payments					763
Liabilities, Issuances					0
Liabilities, Transfers into Level 3					0
Liabilities, Transfers out of Level 3					0
Liabilities, Ending Balance					0
Guarantees [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Liabilities, Begining Balance	0		(828)		0
Liabilities, Accreted Discounts/Amortized Premiums			0		0
Liabilities, Realized Gain/(Loss)			0		0
Liabilities, Change In Net Unrealized Gain/(Loss)			828		(828)
Liabilities, Payments			0		0
Liabilities, Issuances			0		0
Liabilities, Transfers into Level 3			0		0
Liabilities, Transfers out of Level 3			0		0
Liabilities, Ending Balance			0		(828)
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)					(828)
Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	518,250		486,974		626,999
Assets, Accreted Discounts/Amortized Premiums	(26,697)		(16,102)		(20,675)
Assets, Realized Gain (Loss)	4,605		(5,889)		23,659
Assets, Change In Net Unrealized Gain/(Loss)	25,948		(1,407)		(31,735)
Assets, Purchases	638,382		480,146		430,605
Assets, Sales	(452,012)		(421,342)		(500,041)
Assets, Transfers into Level 3	14,021		10,041		6,687
Assets, Transfers out of Level 3	(64,049)		(14,171)		(48,525)
Assets, Ending Balance	658,448		518,250		486,974
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	10,600		(14,700)		(20,700)
Investments [Member] | Agency residential mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	29,622		24,918		31,385
Assets, Accreted Discounts/Amortized Premiums	(9,356)		(7,998)		(8,355)
Assets, Realized Gain (Loss)	(956)		(536)		223
Assets, Change In Net Unrealized Gain/(Loss)	(165)		845		81
Assets, Purchases	3,867		12,665		6,977
Assets, Sales	(153)		(272)		(5,393)
Assets, Transfers into Level 3	0		0		0
Assets, Transfers out of Level 3	(16,686)		0		0
Assets, Ending Balance	6,173		29,622		24,918
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	90,083		116,435		274,369
Assets, Accreted Discounts/Amortized Premiums	2,203		1,896		8,593
Assets, Realized Gain (Loss)	763		(2,748)		20,648
Assets, Change In Net Unrealized Gain/(Loss)	9,498		3,972		(16,429)
Assets, Purchases	68,724		30,065		62,994
Assets, Sales	(54,690)		(55,407)		(191,902)
Assets, Transfers into Level 3	14,021		10,041		6,687
Assets, Transfers out of Level 3	(29,305)		(14,171)		(48,525)
Assets, Ending Balance	101,297		90,083		116,435
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	43,268		34,145		53,311
Assets, Accreted Discounts/Amortized Premiums	469		1,627		3,076
Assets, Realized Gain (Loss)	(3,596)		1,008		2,000
Assets, Change In Net Unrealized Gain/(Loss)	8,654		(6,081)		(4,183)
Assets, Purchases	6,661		24,488		21,382
Assets, Sales	(37,665)		(11,919)		(41,441)
Assets, Transfers into Level 3	0		0		0
Assets, Transfers out of Level 3	(5,444)		0		0
Assets, Ending Balance	12,347		43,268		34,145
Investments [Member] | Commercial Mortgage Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	61,129		66,399		28,309
Assets, Accreted Discounts/Amortized Premiums	921		2,463		1,895
Assets, Realized Gain (Loss)	419		1,920		1,114
Assets, Change In Net Unrealized Gain/(Loss)	1,957		(1,434)		(142)
Assets, Purchases	78,333		39,684		69,778
Assets, Sales	(34,458)		(47,903)		(34,555)
Assets, Transfers into Level 3	0		0		0
Assets, Transfers out of Level 3	0		0		0
Assets, Ending Balance	108,301		61,129		66,399
Investments [Member] | Residential Mortgage Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	84,290		22,089		27,482
Assets, Accreted Discounts/Amortized Premiums	(599)		467		1,363
Assets, Realized Gain (Loss)	1,602		774		2,372
Assets, Change In Net Unrealized Gain/(Loss)	3,536		(800)		(505)
Assets, Purchases	140,535		102,224		19,555
Assets, Sales	(46,892)		(40,464)		(28,178)
Assets, Transfers into Level 3	0		0		0
Assets, Transfers out of Level 3	0		0		0
Assets, Ending Balance	182,472		84,290		22,089
Investments [Member] | Collateralized Loan Obligations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	44,956		45,974		121,994
Assets, Accreted Discounts/Amortized Premiums	(6,833)		(3,829)		(21,110)
Assets, Realized Gain (Loss)	2,233		71		46
Assets, Change In Net Unrealized Gain/(Loss)	2,606		2,471		(4,033)
Assets, Purchases	71,338		27,862		59,102
Assets, Sales	(76,775)		(27,593)		(110,025)
Assets, Transfers into Level 3	0		0		0
Assets, Transfers out of Level 3	(12,614)		0		0
Assets, Ending Balance	24,911		44,956		45,974
Investments [Member] | Consumer loans and asset-backed securities backed by consumer loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	107,157	[1]	115,376	[1]	24,294
Assets, Accreted Discounts/Amortized Premiums	(13,754)		(10,668)	[1]	(6,197)
Assets, Realized Gain (Loss)	855		(164)	[1]	0
Assets, Change In Net Unrealized Gain/(Loss)	(171)		(3,711)	[1]	283
Assets, Purchases	129,525		154,101	[1]	139,373
Assets, Sales	(88,354)		(147,777)	[1]	(42,377)
Assets, Transfers into Level 3	0		0	[1]	0
Assets, Transfers out of Level 3	0		0	[1]	0
Assets, Ending Balance	135,258		107,157	[1]	115,376	[1]
Investments [Member] | Corporate Debt [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	25,004		27,028		42,708
Assets, Accreted Discounts/Amortized Premiums	252		(60)		60
Assets, Realized Gain (Loss)	527		(8,326)		(4,028)
Assets, Change In Net Unrealized Gain/(Loss)	223		6,864		(6,882)
Assets, Purchases	97,466		26,851		28,942
Assets, Sales	(99,525)		(27,353)		(33,772)
Assets, Transfers into Level 3	0		0		0
Assets, Transfers out of Level 3	0		0		0
Assets, Ending Balance	23,947		25,004		27,028
Investments [Member] | Real Estate Owned [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	3,349		12,522		8,635
Assets, Accreted Discounts/Amortized Premiums	0		0		0
Assets, Realized Gain (Loss)	411		2,256		1,168
Assets, Change In Net Unrealized Gain/(Loss)	322		(458)		381
Assets, Purchases	25,516		17,526		14,155
Assets, Sales	(3,321)		(28,497)		(11,817)
Assets, Transfers into Level 3	0		0		0
Assets, Transfers out of Level 3	0		0		0
Assets, Ending Balance	26,277		3,349		12,522
Investments [Member] | Corporate Equity Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	29,392	[1]	22,088	[1]	14,512
Assets, Accreted Discounts/Amortized Premiums	0		0	[1]	0
Assets, Realized Gain (Loss)	2,347		(144)	[1]	116
Assets, Change In Net Unrealized Gain/(Loss)	(512)		(3,075)	[1]	(306)
Assets, Purchases	16,417		44,680	[1]	8,347
Assets, Sales	(10,179)		(34,157)	[1]	(581)
Assets, Transfers into Level 3	0		0	[1]	0
Assets, Transfers out of Level 3	0		0	[1]	0
Assets, Ending Balance	37,465		29,392	[1]	22,088	[1]
Investments Sold Short [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Liabilities, Begining Balance	0		(448)		0
Liabilities, Accreted Discounts/Amortized Premiums			(1)		(2)
Liabilities, Realized Gain/(Loss)			362		197
Liabilities, Change In Net Unrealized Gain/(Loss)			(228)		228
Liabilities, Purchases			315		1,372
Liabilities, Sales			0		(2,243)
Liabilities, Transfers into Level 3			0		0
Liabilities, Transfers out of Level 3			0		0
Liabilities, Ending Balance			0		(448)
Investments Sold Short [Member] | Corporate Debt Sold Short [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Liabilities, Begining Balance	0		(448)		0
Liabilities, Accreted Discounts/Amortized Premiums			(1)		(2)
Liabilities, Realized Gain/(Loss)			362		197
Liabilities, Change In Net Unrealized Gain/(Loss)			(228)		228
Liabilities, Purchases			315		1,372
Liabilities, Sales			0		(2,243)
Liabilities, Transfers into Level 3			0		0
Liabilities, Transfers out of Level 3			0		0
Liabilities, Ending Balance			0		(448)
Financial Derivatives - Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	5,587		6,567		11,487
Assets, Accreted Discounts/Amortized Premiums	0		0		0
Assets, Realized Gain (Loss)	394		4,062		(2,851)
Assets, Change In Net Unrealized Gain/(Loss)	(1,363)		(591)		2,183
Assets, Purchases	138		7,691		78
Assets, Sales	(1,616)		(12,142)		(4,330)
Assets, Transfers into Level 3	0		0		0
Assets, Transfers out of Level 3	0		0		0
Assets, Ending Balance	3,140		5,587		6,567
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(1,200)		(800)		7
Financial Derivatives - Assets [Member] | Total Return Swaps [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	155		85		0
Assets, Accreted Discounts/Amortized Premiums	0		0		0
Assets, Realized Gain (Loss)	224		3,070		113
Assets, Change In Net Unrealized Gain/(Loss)	(155)		70		85
Assets, Purchases	1		57		0
Assets, Sales	(225)		(3,127)		(113)
Assets, Transfers into Level 3	0		0		0
Assets, Transfers out of Level 3	0		0		0
Assets, Ending Balance	0		155		85
Financial Derivatives - Assets [Member] | Warrant [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Beginning Balance	106		150		100
Assets, Accreted Discounts/Amortized Premiums	0		0		0
Assets, Realized Gain (Loss)	(100)		(50)		0
Assets, Change In Net Unrealized Gain/(Loss)	(6)		6		0
Assets, Purchases	0		7,486		50
Assets, Sales	0		(7,486)		0
Assets, Transfers into Level 3	0		0		0
Assets, Transfers out of Level 3	0		0		0
Assets, Ending Balance	0		106		150
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	5,326		6,332		11,387
Assets, Accreted Discounts/Amortized Premiums	0		0		0
Assets, Realized Gain (Loss)	270		1,042		(2,964)
Assets, Change In Net Unrealized Gain/(Loss)	(1,202)		(667)		2,098
Assets, Purchases	137		148		28
Assets, Sales	(1,391)		(1,529)		(4,217)
Assets, Transfers into Level 3	0		0		0
Assets, Transfers out of Level 3	0		0		0
Assets, Ending Balance	3,140		5,326		6,332
Financial Derivatives - Liabilities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Liabilities, Begining Balance	(505)		(4,883)		(239)
Liabilities, Accreted Discounts/Amortized Premiums	0		0		0
Liabilities, Realized Gain/(Loss)	(1,425)		(7,857)		2,414
Liabilities, Change In Net Unrealized Gain/(Loss)	1,188		4,377		(4,627)
Liabilities, Purchases	1,308		8,538		14
Liabilities, Sales	(566)		(680)		(2,445)
Liabilities, Transfers into Level 3	0		0		0
Liabilities, Transfers out of Level 3	0		0		0
Liabilities, Ending Balance	0		(505)		(4,883)
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)			(200)		(4,600)
Financial Derivatives - Liabilities [Member] | Total Return Swaps [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Liabilities, Begining Balance	(249)		(4,662)		0
Liabilities, Accreted Discounts/Amortized Premiums	0		0		0
Liabilities, Realized Gain/(Loss)	(554)		(7,534)		2,516
Liabilities, Change In Net Unrealized Gain/(Loss)	249		4,413		(4,662)
Liabilities, Purchases	572		8,214		14
Liabilities, Sales	(18)		(680)		(2,530)
Liabilities, Transfers into Level 3	0		0		0
Liabilities, Transfers out of Level 3	0		0		0
Liabilities, Ending Balance	0		(249)		(4,662)
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	(256)		(221)		(239)
Liabilities, Accreted Discounts/Amortized Premiums	0		0		0
Liabilities, Realized Gain/(Loss)	(871)		(323)		(102)
Liabilities, Change In Net Unrealized Gain/(Loss)	939		(36)		35
Liabilities, Purchases	736		324		0
Liabilities, Sales	(548)		0		85
Liabilities, Transfers into Level 3	0		0		0
Liabilities, Transfers out of Level 3	0		0		0
Liabilities, Ending Balance	$ 0		$ (256)		$ (221)

[1] Conformed to current period presentation.