Financial Derivatives (Schedule of Gains and Losses on Derivative Contracts) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Net Realized Gains (Losses) on Periodic Settlements of Interest Rate Swaps	$ 1,695
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	(32,562)
Realized gains (losses) on financial derivatives, net	(30,867)	$ 1,911
Change in Net Unrealized Gains (Losses) on Accrued Periodic Settlements of Interest Rate Swaps	(764)
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	(4,573)
Unrealized gains (losses) on financial derivatives, net	(5,337)	7,807
Foreign currency transactions	(2,392)	4,131
Foreign currency translation		(7,071)
Derivative [Member]
Derivative [Line Items]
Foreign currency transactions	45	100
Foreign currency translation	1	100
Interest rate swaps | Interest Rate Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) on Periodic Settlements of Interest Rate Swaps	1,695
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	(876)
Realized gains (losses) on financial derivatives, net	819	(985)
Change in Net Unrealized Gains (Losses) on Accrued Periodic Settlements of Interest Rate Swaps	(764)
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	(5,778)
Unrealized gains (losses) on financial derivatives, net	(6,542)	3,648
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	528
Realized gains (losses) on financial derivatives, net	528	(687)
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	(479)
Unrealized gains (losses) on financial derivatives, net	(479)	715
Credit default swaps on asset-backed indices | Credit Risk [Member]
Derivative [Line Items]
Realized gains (losses) on financial derivatives, net		(2,293)
Unrealized gains (losses) on financial derivatives, net		2,013
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	(1,883)
Realized gains (losses) on financial derivatives, net	(1,883)
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	(1,848)
Unrealized gains (losses) on financial derivatives, net	(1,848)
Credit default swaps on corporate bond indices | Credit Risk [Member]
Derivative [Line Items]
Realized gains (losses) on financial derivatives, net		(1,983)
Unrealized gains (losses) on financial derivatives, net		3,540
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	(5,262)
Realized gains (losses) on financial derivatives, net	(5,262)
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	(1,364)
Unrealized gains (losses) on financial derivatives, net	(1,364)
Credit default swaps on corporate bonds | Credit Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	(708)
Realized gains (losses) on financial derivatives, net	(708)	2,993
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	1,007
Unrealized gains (losses) on financial derivatives, net	1,007	(2,648)
Total return swaps | Equity Market/Credit Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	(1,460)
Realized gains (losses) on financial derivatives, net	(1,460)	3,844
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	(584)
Unrealized gains (losses) on financial derivatives, net	(584)	(5)
TBA securities | Interest Rate Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	(15,755)
Realized gains (losses) on financial derivatives, net	(15,755)
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	4,026
Unrealized gains (losses) on financial derivatives, net	4,026
Futures | Interest Rate/Currency Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	(7,924)
Realized gains (losses) on financial derivatives, net	(7,924)	162
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	458
Unrealized gains (losses) on financial derivatives, net	458	108
Forwards | Currency risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	813
Realized gains (losses) on financial derivatives, net	813	923
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	(12)
Unrealized gains (losses) on financial derivatives, net	(12)	359
Options | Interest Rate Risk [Member]
Derivative [Line Items]
Net Realized Gains (Losses) Other Than Periodic Settlements of Interest Rate Swaps	(35)
Realized gains (losses) on financial derivatives, net	(35)
Change in Net Unrealized Gains (Losses) Other Than on Accrued Periodic Settlements of Interest Rate Swaps	1
Unrealized gains (losses) on financial derivatives, net	$ 1
Options | Interest Rates/Equity Market Risk [Member]
Derivative [Line Items]
Realized gains (losses) on financial derivatives, net		(63)
Unrealized gains (losses) on financial derivatives, net		$ 77