Consolidated Condensed Schedule of Investments (Investments Sold Short) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019
Investments Sold, Not yet Purchased [Line Items]
Securities sold short, at fair value	$ (850,577)	$ (38,642)	$ (73,409)
Investment Sold, Not yet Purchased, Sale Proceeds	(844,604)
TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal			$ (753,697)
Securities sold short, at fair value	$ (772,964)
Investment Sold, Not yet Purchased, Percent of Net Assets	(129.87%)
Investment Sold, Not yet Purchased, Sale Proceeds	$ (766,777)
Common stock
Investments Sold, Not yet Purchased [Line Items]
Securities sold short, at fair value	$ (16,933)
Investment Sold, Not yet Purchased, Percent of Net Assets	(2.84%)
Investment Sold, Not yet Purchased, Sale Proceeds	$ (17,164)
Corporate debt securities
Investments Sold, Not yet Purchased [Line Items]
Securities sold short, at fair value	$ (6,529)
Investment Sold, Not yet Purchased, Percent of Net Assets	(1.10%)
Investment Sold, Not yet Purchased, Sale Proceeds	$ (6,708)
Investments Sold Short
Investments Sold, Not yet Purchased [Line Items]
Securities sold short, at fair value	$ (850,577)
Investment Sold, Not yet Purchased, Percent of Net Assets	(142.91%)
Investment Sold, Not yet Purchased, Sale Proceeds	$ (844,604)
Government debt
Investments Sold, Not yet Purchased [Line Items]
Securities sold short, at fair value	$ (54,151)
Investment Sold, Not yet Purchased, Percent of Net Assets	(9.10%)
Investment Sold, Not yet Purchased, Sale Proceeds	$ (53,955)
Federal National Mortgage Association [Member] | TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Investment Sold, Not yet Purchased, Percent of Net Assets	(66.31%)
Federal Home Loan Mortgage Corporation [Member] | TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Investment Sold, Not yet Purchased, Percent of Net Assets	(22.71%)
Government National Mortgage Association [Member] | TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Investment Sold, Not yet Purchased, Percent of Net Assets	(40.85%)
North America [Member] | US Government Debt Securities [Member]
Investments Sold, Not yet Purchased [Line Items]
Securities sold short, at fair value	$ (34,817)
Investment Sold, Not yet Purchased, Percent of Net Assets	(5.85%)
Investment Sold, Not yet Purchased, Sale Proceeds	$ (34,410)
North America [Member] | Mortgage-related Residential [Member] | Federal National Mortgage Association (30 Year) 4 Point 50 Percent [Member] | TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (156,590)
Investment Interest Rate	4.50%
Securities sold short, at fair value	$ (162,119)
Investments maturity date	2019-01
North America [Member] | Mortgage-related Residential [Member] | Government National Mortgage Association (30 Year) 4 Point 50 Percent [Member] | TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (117,590)
Investment Interest Rate	4.50%
Securities sold short, at fair value	$ (121,637)
Investments maturity date	2019-01
North America [Member] | Mortgage-related Residential [Member] | Federal Home Loan Mortgage Corporation (30 Year) 4 Point 00 Percent [Member] | TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (107,397)
Investment Interest Rate	4.00%
Securities sold short, at fair value	$ (109,465)
Investments maturity date	2019-01
North America [Member] | Mortgage-related Residential [Member] | Federal National Mortgage Association (30 Year) 5 Point 00 Percent [Member] | TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (87,817)
Investment Interest Rate	5.00%
Securities sold short, at fair value	$ (91,971)
Investments maturity date	2019-01
North America [Member] | Mortgage-related Residential [Member] | Government National Mortgage Association (30 Year) 4 Point 00 Percent [Member] | TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (86,893)
Investment Interest Rate	4.00%
Securities sold short, at fair value	$ (88,994)
Investments maturity date	2019-01
North America [Member] | Mortgage-related Residential [Member] | Federal National Mortgage Association (30 Year) 3 Point 50 Percent [Member] | TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (76,912)
Investment Interest Rate	3.50%
Securities sold short, at fair value	$ (76,891)
Investments maturity date	2019-01
North America [Member] | Mortgage-related Residential [Member] | Government National Mortgage Association (30 Year) 3 Point 50 Percent [Member] | TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (32,260)
Investment Interest Rate	3.50%
Securities sold short, at fair value	$ (32,484)
Investments maturity date	2019-01
North America [Member] | Mortgage-related Residential [Member] | Federal National Mortgage Association (15 Year) 3 Point 50 Percent [Member] | TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (26,530)
Investment Interest Rate	3.50%
Securities sold short, at fair value	$ (26,859)
Investments maturity date	2019-01
North America [Member] | Mortgage-related Residential [Member] | Federal Home Loan Mortgage Corporation (30 Year) 4 Point 50 Percent [Member] | TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (24,841)
Investment Interest Rate	4.50%
Securities sold short, at fair value	$ (25,707)
Investments maturity date	2019-01
North America [Member] | Mortgage-related Residential [Member] | Federal National Mortgage Association (30 Year) 3 Point 00 Percent [Member] | TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (16,557)
Investment Interest Rate	3.00%
Securities sold short, at fair value	$ (16,153)
Investments maturity date	2019-01
North America [Member] | Mortgage-related Residential [Member] | Federal National Mortgage Association (15 Year) 3 Point 00 Percent [Member] | TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (13,450)
Investment Interest Rate	3.00%
Securities sold short, at fair value	$ (13,426)
Investments maturity date	2019-01
North America [Member] | Mortgage-related Residential [Member] | Federal National Mortgage Association (30 Year) 5 Point 50 Percent [Member] | TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (6,860)
Investment Interest Rate	5.50%
Securities sold short, at fair value	$ (7,258)
Investments maturity date	2019-01
North America [Member] | Government Sector [Member] | U.S. Treasury Note, 2.88 Percent, Maturity Date 2021 11 [Member] [Domain] | US Government Debt Securities [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (13,600)
Investment Interest Rate	2.88%
Securities sold short, at fair value	$ (13,754)
Investments maturity date	2021-11
North America [Member] | Government Sector [Member] | U.S. Treasury Note, 2.88 Percent, Maturity Date 2023 10 [Member] [Domain] | US Government Debt Securities [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (10,451)
Investment Interest Rate	2.88%
Securities sold short, at fair value	$ (10,631)
Investments maturity date	2023-10
North America [Member] | Government Sector [Member] | U.S. Treasury Note, 3.13 Percent, Maturity Date 2028 11 [Member] [Domain] | US Government Debt Securities [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (3,400)
Investment Interest Rate	3.13%
Securities sold short, at fair value	$ (3,528)
Investments maturity date	2028-11
North America [Member] | Government Sector [Member] | U.S. Treasury Note, 2.88 Percent, Maturity Date 2028 08 [Member] | US Government Debt Securities [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (2,800)
Investment Interest Rate	2.88%
Securities sold short, at fair value	$ (2,844)
Investments maturity date	2028-08
North America [Member] | Government Sector [Member] | U.S. Treasury Note, 2.88 Percent, Maturity Date 2023 11 [Member] [Domain] | US Government Debt Securities [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (2,062)
Investment Interest Rate	2.88%
Securities sold short, at fair value	$ (2,098)
Investments maturity date	2023-11
North America [Member] | Government Sector [Member] | U.S. Treasury Note, 2.75 Percent, Maturity Date 2023 08 [Member] | US Government Debt Securities [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (1,939)
Investment Interest Rate	2.75%
Securities sold short, at fair value	$ (1,962)
Investments maturity date	2023-08
North America [Member] | Financial [Member] | Exchange Traded Equity [Member] | Common stock
Investments Sold, Not yet Purchased [Line Items]
Securities sold short, at fair value	$ (16,933)
Investment Sold, Not yet Purchased, Balance, Shares	(277)
North America [Member] | Financial [Member] | Various Issuer [Member] | Corporate debt securities
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (3,600)
Securities sold short, at fair value	$ (2,810)
North America [Member] | Financial [Member] | Various Issuer [Member] | Corporate debt securities | Minimum
Investments Sold, Not yet Purchased [Line Items]
Investment Interest Rate	4.70%
Investments maturity date	2026-12
North America [Member] | Financial [Member] | Various Issuer [Member] | Corporate debt securities | Maximum
Investments Sold, Not yet Purchased [Line Items]
Investment Interest Rate	5.95%
Investments maturity date	2027-06
North America [Member] | Communications [Member] | Various Issuer [Member] | Corporate debt securities
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (1,730)
Investment Interest Rate	4.25%
Securities sold short, at fair value	$ (1,734)
Investments maturity date	2023-09
North America [Member] | Consumer [Member] | Various Issuer [Member] | Corporate debt securities
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (500)
Investment Interest Rate	5.75%
Securities sold short, at fair value	$ (500)
Investments maturity date	2022-10
North America [Member] | Energy [Member] | Various Issuer [Member] | Corporate debt securities
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (2,000)
Investment Interest Rate	9.88%
Securities sold short, at fair value	$ (1,230)
Investments maturity date	2024-02
North America [Member] | Technology Sector [Member] | Various Issuer [Member] | Corporate debt securities
Investments Sold, Not yet Purchased [Line Items]
Current Principal	$ (288)
Investment Interest Rate	4.95%
Securities sold short, at fair value	$ (255)
Investments maturity date	2023-04
Europe [Member] | Debt Security, Government, Non-US [Member]
Investments Sold, Not yet Purchased [Line Items]
Securities sold short, at fair value	$ (19,334)
Investment Sold, Not yet Purchased, Percent of Net Assets	(3.25%)
Investment Sold, Not yet Purchased, Sale Proceeds	$ (19,545)
Europe [Member] | Government Sector [Member] | European Sovereign Bond [Member] | Debt Security, Government, Non-US [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal	(19,006)
Securities sold short, at fair value	$ (19,334)
Europe [Member] | Government Sector [Member] | European Sovereign Bond [Member] | Debt Security, Government, Non-US [Member] | Minimum
Investments Sold, Not yet Purchased [Line Items]
Investment Interest Rate	0.75%
Investments maturity date	2019-04
Europe [Member] | Government Sector [Member] | European Sovereign Bond [Member] | Debt Security, Government, Non-US [Member] | Maximum
Investments Sold, Not yet Purchased [Line Items]
Investment Interest Rate	2.75%
Investments maturity date	2021-07