Financial Derivatives (Schedule of Gains and Losses on Derivative Contracts) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Derivative [Line Items]
Net Realized Gains (Losses) on Periodic Settlements of Interest Rate Swaps	$ 77	$ (892)	$ (739)	$ (750)
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	348	(10,771)	6,977	(23,306)
Realized gains (losses) on financial derivatives, net	425	(11,663)	6,238	(24,056)
Change in Net Unrealized Gains (Losses) on Accrued Periodic Settlements of Interest Rate Swaps	(709)	136	(299)	25
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	(4,971)	8,040	5,297	(1,817)
Unrealized gains (losses) on financial derivatives, net	(5,680)	8,176	4,998	(1,792)
Derivative [Member]
Derivative [Line Items]
Foreign currency transactions		13	18	26
Foreign currency translation	3	3	(30)	19
Interest rate swaps | Interest Rate Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) on Periodic Settlements of Interest Rate Swaps	77	(892)	(739)	(750)
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	(300)	(2,348)	147	(8,732)
Realized gains (losses) on financial derivatives, net	(223)	(3,240)	(592)	(9,482)
Change in Net Unrealized Gains (Losses) on Accrued Periodic Settlements of Interest Rate Swaps	(709)	136	(299)	25
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	(4,221)	2,543	3,454	(17,477)
Unrealized gains (losses) on financial derivatives, net	(4,930)	2,679	3,155	(17,452)
Credit default swaps on asset-backed securities | Credit Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	16	38	42	(956)
Realized gains (losses) on financial derivatives, net	16	38	42	(956)
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	(18)	(1)	(44)	916
Unrealized gains (losses) on financial derivatives, net	(18)	(1)	(44)	916
Credit default swaps on corporate bond indices | Credit Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	129	4,455	1,199	3,899
Realized gains (losses) on financial derivatives, net	129	4,455	1,199	3,899
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	(221)	(5,384)	(1,178)	7,139
Unrealized gains (losses) on financial derivatives, net	(221)	(5,384)	(1,178)	7,139
Credit default swaps on corporate bond indices | Credit Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	836	(62)	(88)	517
Realized gains (losses) on financial derivatives, net	836	(62)	(88)	517
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	(1,418)	24	(890)	4,140
Unrealized gains (losses) on financial derivatives, net	(1,418)	24	(890)	4,140
Credit default swaps on corporate bonds | Credit Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	153	354	81	448
Realized gains (losses) on financial derivatives, net	153	354	81	448
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	(219)	(482)	(153)	1,044
Unrealized gains (losses) on financial derivatives, net	(219)	(482)	(153)	1,044
Total return swaps | Credit Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	(860)	(484)	(1,202)	(2,055)
Realized gains (losses) on financial derivatives, net	(860)	(484)	(1,202)	(2,055)
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	801	1,168	940	955
Unrealized gains (losses) on financial derivatives, net	801	1,168	940	955
TBA securities | Interest Rate Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	(358)	(5,972)	4,961	(9,145)
Realized gains (losses) on financial derivatives, net	(358)	(5,972)	4,961	(9,145)
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	2,365	7,447	1,661	2,024
Unrealized gains (losses) on financial derivatives, net	2,365	7,447	1,661	2,024
Futures | Interest Rate Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	896	(6,342)	1,913	(7,464)
Realized gains (losses) on financial derivatives, net	896	(6,342)	1,913	(7,464)
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	(2,037)	5,629	878	(485)
Unrealized gains (losses) on financial derivatives, net	(2,037)	5,629	878	(485)
Forwards | Currency risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	(164)	(310)	(76)	282
Realized gains (losses) on financial derivatives, net	(164)	(310)	(76)	282
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	98	56	725	309
Unrealized gains (losses) on financial derivatives, net	98	56	725	309
Warrants | Equity Market/Credit Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	0	0	0	0
Realized gains (losses) on financial derivatives, net	0	0	0	0
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	(39)	(402)	(34)	(382)
Unrealized gains (losses) on financial derivatives, net	(39)	(402)	(34)	(382)
Options | Interest Rate Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps				(100)
Realized gains (losses) on financial derivatives, net				(100)
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps				0
Unrealized gains (losses) on financial derivatives, net				$ 0
Options | Equity Market/Credit Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps		(100)
Realized gains (losses) on financial derivatives, net		(100)
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps		(2,558)
Unrealized gains (losses) on financial derivatives, net		$ (2,558)
Put Option [Member] | Interest Rate Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	0
Realized gains (losses) on financial derivatives, net	0
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	(62)
Unrealized gains (losses) on financial derivatives, net	$ (62)
Put Option [Member] | Credit Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps			0
Realized gains (losses) on financial derivatives, net			0
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps			(62)
Unrealized gains (losses) on financial derivatives, net			$ (62)