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

[1] At December 31, 2018, the Company's short investments guaranteed by the Federal National Mortgage Association, the Federal Home Loan Mortgage Corporation, and the Government National Mortgage Association, represented 66.31%, 22.71%, and 40.85% of Total Equity, respectively.

[2] Classification percentages are based on Total Equity.

[3] See Note 2 and Note 3 in Notes to Consolidated Financial Statements.