Consolidated Condensed Schedule Of Investments (Investments Sold Short) - USD ($) shares in Thousands, $ in Thousands		9 Months Ended		12 Months Ended
		Sep. 30, 2017		Dec. 31, 2016
Investments Sold, Not yet Purchased [Line Items]
Investments sold short, at fair value-		$ (675,650)		$ (584,896)
Proceeds from investments sold short		$ 672,506		$ 589,429
TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Investment Sold, Not yet Purchased, Percent of Equity		(74.71%)	[1],[2],[3]	(62.77%)	[4],[5],[6]
Current Principal/Notional Amount		$ (447,590)		$ (384,155)
Investments sold short, at fair value-		(470,487)	[1],[3]	(404,728)	[4],[6]
Proceeds from investments sold short		(471,204)	[1],[3]	(404,967)	[4],[6]
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		$ (65,000)	[1],[3]	$ (50,930)	[4],[6]
Rate		4.50%	[1],[3]	4.50%	[4],[6]
Investments maturity date		2017-11	[1],[3]	2017-01	[4],[6]
Investments sold short, at fair value-		$ (69,695)	[1],[3]	$ (54,748)	[4],[6]
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		$ (64,000)	[1],[3]	$ (87,767)	[4],[6]
Rate		4.00%	[1],[3]	4.00%	[4],[6]
Investments maturity date		2017-11	[1],[3]	2017-01	[4],[6]
Investments sold short, at fair value-		$ (67,280)	[1],[3]	$ (92,210)	[4],[6]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 4.00% [Member] | Mortgage-related Residential [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount		$ (60,000)	[1],[3]	$ (26,000)	[4],[6]
Rate		4.00%	[1],[3]	4.00%	[4],[6]
Investments maturity date		2017-11	[1],[3]	2017-02	[4],[6]
Investments sold short, at fair value-		$ (63,077)	[1],[3]	$ (27,295)	[4],[6]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 3.50% [Member] | Mortgage-related Residential [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount		$ (45,188)	[1],[3]	$ (24,352)	[4],[6]
Rate		3.50%	[1],[3]	3.50%	[4],[6]
Investments maturity date		2017-10	[1],[3]	2017-01	[4],[6]
Investments sold short, at fair value-		$ (46,588)	[1],[3]	$ (24,960)	[4],[6]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 4 Point 00 Percent 201710 [Member] | Mortgage-related Residential [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[1],[3]	$ (43,187)
Rate	[1],[3]	4.00%
Investments maturity date	[1],[3]	2017-10
Investments sold short, at fair value-	[1],[3]	$ (45,469)
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 4 Point 50 Percent 201710 [Member] | Mortgage-related Residential [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[1],[3]	$ (35,730)
Rate	[1],[3]	4.50%
Investments maturity date	[1],[3]	2017-10
Investments sold short, at fair value-	[1],[3]	$ (38,352)
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 3 Point 50 Percent 201711 [Member] | Mortgage-related Residential [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[1],[3]	$ (36,000)
Rate	[1],[3]	3.50%
Investments maturity date	[1],[3]	2017-11
Investments sold short, at fair value-	[1],[3]	$ (37,049)
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal Home Loan Mortgage Corporation (30 Year) 4 Point 00 Percent 201710 [Member] | Mortgage-related Residential [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[1],[3]	$ (23,467)
Rate	[1],[3]	4.00%
Investments maturity date	[1],[3]	2017-10
Investments sold short, at fair value-	[1],[3]	$ (24,705)
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (15 Year) 3.00% [Member] | Mortgage-related Residential [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount		$ (21,520)	[1],[3]	$ (20,740)	[4],[6]
Rate		3.00%	[1],[3]	3.00%	[4],[6]
Investments maturity date		2017-10	[1],[3]	2017-01	[4],[6]
Investments sold short, at fair value-		$ (22,113)	[1],[3]	$ (21,285)	[4],[6]
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	[4],[6]			$ (15,770)
Rate	[4],[6]			4.50%
Investments maturity date	[4],[6]			2017-01
Investments sold short, at fair value-	[4],[6]			$ (17,058)
TBA - Fixed Rate Agency Securities Sold Short [Member] | Government National Mortgage Association (30 Year) 3 Point 50 Percent 201710 [Member] | Mortgage-related Residential [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[1],[3]	$ (12,810)
Rate	[1],[3]	3.50%
Investments maturity date	[1],[3]	2017-10
Investments sold short, at fair value-	[1],[3]	$ (13,317)
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)	[1],[3]	$ (6,860)	[4],[6]
Rate		5.50%	[1],[3]	5.50%	[4],[6]
Investments maturity date		2017-10	[1],[3]	2017-01	[4],[6]
Investments sold short, at fair value-		$ (7,591)	[1],[3]	$ (7,622)	[4],[6]
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		$ (6,951)	[1],[3]	$ (23,151)	[4],[6]
Rate		4.50%	[1],[3]	4.50%	[4],[6]
Investments maturity date		2017-10	[1],[3]	2017-01	[4],[6]
Investments sold short, at fair value-		$ (7,453)	[1],[3]	$ (24,840)	[4],[6]
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		$ (7,112)	[1],[3]	$ (4,612)	[4],[6]
Rate		3.00%	[1],[3]	3.00%	[4],[6]
Investments maturity date		2017-10	[1],[3]	2017-01	[4],[6]
Investments sold short, at fair value-		$ (7,135)	[1],[3]	$ (4,584)	[4],[6]
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	[1],[3]	$ (6,700)
Rate	[1],[3]	3.50%
Investments maturity date	[1],[3]	2017-10
Investments sold short, at fair value-	[1],[3]	$ (6,978)
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		$ (5,680)	[1],[3]	$ (31,620)	[4],[6]
Rate		5.00%	[1],[3]	5.00%	[4],[6]
Investments maturity date		2017-10	[1],[3]	2017-01	[4],[6]
Investments sold short, at fair value-		$ (6,199)	[1],[3]	$ (34,426)	[4],[6]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal Home Loan Mortgage Corporation (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		$ (5,515)	[1],[3]	$ (3,155)	[4],[6]
Rate		3.00%	[1],[3]	3.00%	[4],[6]
Investments maturity date		2017-10	[1],[3]	2017-01	[4],[6]
Investments sold short, at fair value-		$ (5,532)	[1],[3]	$ (3,134)	[4],[6]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal Home Loan Mortgage Corporation (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		$ (1,870)	[1],[3]	$ (8,790)	[4],[6]
Rate		3.50%	[1],[3]	3.50%	[4],[6]
Investments maturity date		2017-10	[1],[3]	2017-01	[4],[6]
Investments sold short, at fair value-		$ (1,954)	[1],[3]	$ (9,169)	[4],[6]
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	[4],[6]			$ (21,940)
Rate	[4],[6]			3.50%
Investments maturity date	[4],[6]			2017-01
Investments sold short, at fair value-	[4],[6]			$ (22,819)
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	[4],[6]			$ (1,700)
Rate	[4],[6]			4.00%
Investments maturity date	[4],[6]			2017-01
Investments sold short, at fair value-	[4],[6]			$ (1,806)
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal Home Loan Mortgage Corporation (15 Year) 3 Percent [Member] | Mortgage-related Residential [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[4],[6]			$ (13,510)
Rate	[4],[6]			3.00%
Investments maturity date	[4],[6]			2017-01
Investments sold short, at fair value-	[4],[6]			$ (13,869)
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (15 Year) 4 Percent [Member] | Mortgage-related Residential [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[4],[6]			$ (11,170)
Rate	[4],[6]			4.00%
Investments maturity date	[4],[6]			2017-01
Investments sold short, at fair value-	[4],[6]			$ (11,494)
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 4.00% 2017 01 [Member] | Mortgage-related Residential [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[4],[6]			$ (20,558)
Rate	[4],[6]			4.00%
Investments maturity date	[4],[6]			2017-01
Investments sold short, at fair value-	[4],[6]			$ (21,611)
TBA - Fixed Rate Agency Securities Sold Short [Member] | Government National Mortgage Association (30 Year) 3.00% [Member] | Mortgage-related Residential [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[4],[6]			$ (6,500)
Rate	[4],[6]			3.00%
Investments maturity date	[4],[6]			2017-01
Investments sold short, at fair value-	[4],[6]			$ (6,568)
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (15 Year) 3.50% [Member] | Mortgage-related Residential [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[4],[6]			$ (2,530)
Rate	[4],[6]			3.50%
Investments maturity date	[4],[6]			2017-02
Investments sold short, at fair value-	[4],[6]			$ (2,633)
TBA - Fixed Rate Agency Securities Sold Short [Member] | Government National Mortgage Association (30 Year) 3.50% 2017 02 [Member] | Mortgage-related Residential [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[4],[6]			$ (2,500)
Rate	[4],[6]			3.50%
Investments maturity date	[4],[6]			2017-02
Investments sold short, at fair value-	[4],[6]			$ (2,597)
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		(55.62%)		(32.67%)
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		(16.98%)		(22.21%)
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		(2.11%)		(7.89%)
US Government Debt Securities [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Investment Sold, Not yet Purchased, Percent of Equity		(8.01%)	[2],[3]	(10.82%)	[5],[6]
Investments sold short, at fair value-		$ (50,467)	[3]	$ (69,762)	[6]
Proceeds from investments sold short		(50,523)	[3]	(69,946)	[6]
US Government Debt Securities [Member] | U.S. Treasury Note, 2.25 Percent, Maturity Date 2027 02 [Member] | Government [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[3]	$ (30,501)
Rate	[3]	2.25%
Investments maturity date	[3]	2027-02
Investments sold short, at fair value-	[3]	$ (30,320)
US Government Debt Securities [Member] | US Treasury Note, 1.75 Percent, Maturity Date 2022 05 [Member] | Government [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[3]	$ (6,560)
Rate	[3]	1.75%
Investments maturity date	[3]	2022-05
Investments sold short, at fair value-	[3]	$ (6,517)
US Government Debt Securities [Member] | U.S. Treasury Note, 2.00 Percent, Maturity Date 2026 11 [Member] | Government [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount		$ (5,633)	[3]	$ (48,133)	[6]
Rate		2.00%	[3]	2.00%	[6]
Investments maturity date		2026-11	[3]	2026-11	[6]
Investments sold short, at fair value-		$ (5,490)	[3]	$ (46,287)	[6]
US Government Debt Securities [Member] | U.S. Treasury Note, 2.25 Percent, Maturity Date 2027 08 [Member] | Government [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[3]	$ (4,715)
Rate	[3]	2.25%
Investments maturity date	[3]	2027-08
Investments sold short, at fair value-	[3]	$ (4,684)
US Government Debt Securities [Member] | US Treasury Note, 2.38 Percent, Maturity Date 2027 02 [Member] | Government [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[3]	$ (1,869)
Rate	[3]	2.38%
Investments maturity date	[3]	2027-02
Investments sold short, at fair value-	[3]	$ (1,877)
US Government Debt Securities [Member] | US Treasury Note, 1.63 Percent, Maturity Date 2022 08 [Member] | Government [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[3]	$ (1,350)
Rate	[3]	1.63%
Investments maturity date	[3]	2022-08
Investments sold short, at fair value-	[3]	$ (1,332)
US Government Debt Securities [Member] | U.S. Treasury Bond, 2.25 Percent, Maturity Date 2046 08 [Member] | Government [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[3]	$ (281)
Rate	[3]	2.25%
Investments maturity date	[3]	2046-08
Investments sold short, at fair value-	[3]	$ (247)
US Government Debt Securities [Member] | US Treasury Note, 1.38 Percent, Maturity Date 2021 04 [Member] | Government [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[6]			$ (1,305)
Rate	[6]			1.38%
Investments maturity date	[6]			2021-04
Investments sold short, at fair value-	[6]			$ (1,280)
US Government Debt Securities [Member] | US Treasury Note, 1.25 Percent, Maturity Date 2021 10 [Member] | Government [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[6]			$ (800)
Rate	[6]			1.25%
Investments maturity date	[6]			2021-10
Investments sold short, at fair value-	[6]			$ (776)
US Government Debt Securities [Member] | US Treasury Note, 1.13 Percent, Maturity Date 2021 07 [Member] | Government [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[6]			$ (549)
Rate	[6]			1.13%
Investments maturity date	[6]			2021-07
Investments sold short, at fair value-	[6]			$ (531)
US Government Debt Securities [Member] | US Treasury Note, 1.13 Percent, Maturity Date 2021 09 [Member] | Government [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[6]			$ (1,968)
Rate	[6]			1.13%
Investments maturity date	[6]			2021-09
Investments sold short, at fair value-	[6]			$ (1,898)
US Government Debt Securities [Member] | US Treasury Note, 1.50 Percent, Maturity Date 2026 08 [Member] | Government [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[6]			$ (12,160)
Rate	[6]			1.50%
Investments maturity date	[6]			2026-08
Investments sold short, at fair value-	[6]			$ (11,179)
US Government Debt Securities [Member] | US Treasury Note, 1.75 Percent, Maturity Date 2021 11 [Member] | Government [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[6]			$ (4,726)
Rate	[6]			1.75%
Investments maturity date	[6]			2021-11
Investments sold short, at fair value-	[6]			$ (4,690)
US Government Debt Securities [Member] | US Treasury Note, 1.13 Percent, Maturity Date 2021 08 [Member] | Government [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[6]			$ (3,230)
Rate	[6]			1.13%
Investments maturity date	[6]			2021-08
Investments sold short, at fair value-	[6]			$ (3,121)
Foreign Government Debt Securities [Member] | Europe [Member]
Investments Sold, Not yet Purchased [Line Items]
Investment Sold, Not yet Purchased, Percent of Equity		(11.11%)	[2],[3]	(9.72%)	[5],[6]
Investments sold short, at fair value-		$ (69,940)	[3]	$ (62,680)	[6]
Proceeds from investments sold short		(66,592)	[3]	(66,800)	[6]
Foreign Government Debt Securities [Member] | Sovereign Debt Securities [Member] | Government [Member] | Europe [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount		$ (23,262)	[3]	$ (20,754)	[6]
Investments maturity date		2020-11	[3]	2020-11	[6]
Investments sold short, at fair value-		$ (23,691)	[3]	$ (21,219)	[6]
Foreign Government Debt Securities [Member] | Sovereign Debt Securities [Member] | Government [Member] | Europe [Member] | Minimum [Member]
Investments Sold, Not yet Purchased [Line Items]
Rate		0.25%	[3]	0.25%	[6]
Foreign Government Debt Securities [Member] | Sovereign Debt Securities [Member] | Government [Member] | Europe [Member] | Maximum [Member]
Investments Sold, Not yet Purchased [Line Items]
Rate		0.65%	[3]	0.65%	[6]
Foreign Government Debt Securities [Member] | Spanish Sovereign Bond, 0.25 Percent [Member] | Government [Member] | Europe [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount		$ (16,260)	[3]	$ (14,507)	[6]
Rate		0.25%	[3]	0.25%	[6]
Investments maturity date		2018-04	[3]	2018-04	[6]
Investments sold short, at fair value-		$ (16,318)	[3]	$ (14,614)	[6]
Foreign Government Debt Securities [Member] | Spanish Sovereign Bond, 0.75 Percent [Member] | Government [Member] | Europe [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount		$ (10,285)	[3]	$ (9,176)	[6]
Rate		0.75%	[3]	0.75%	[6]
Investments maturity date		2021-07	[3]	2021-07	[6]
Investments sold short, at fair value-		$ (10,560)	[3]	$ (9,379)	[6]
Foreign Government Debt Securities [Member] | Spanish Sovereign Bond, 2.75 Percent [Member] | Government [Member] | Europe [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount		$ (9,328)	[3]	$ (8,322)	[6]
Rate		2.75%	[3]	2.75%	[6]
Investments maturity date		2019-04	[3]	2019-04	[6]
Investments sold short, at fair value-		$ (9,783)	[3]	$ (8,888)	[6]
Foreign Government Debt Securities [Member] | Spanish Sovereign Bond, 1.15 Percent [Member] | Government [Member] | Europe [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount		$ (9,254)	[3]	$ (8,257)	[6]
Rate		1.15%	[3]	1.15%	[6]
Investments maturity date		2020-07	[3]	2020-07	[6]
Investments sold short, at fair value-		$ (9,588)	[3]	$ (8,580)	[6]
Government debt [Member]
Investments Sold, Not yet Purchased [Line Items]
Investment Sold, Not yet Purchased, Percent of Equity		(19.12%)	[2],[3]	(20.54%)	[5],[6]
Investments sold short, at fair value-		$ (120,407)	[3]	$ (132,442)	[6]
Proceeds from investments sold short		$ (117,115)	[3]	$ (136,746)	[6]
Common Stock Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Investment Sold, Not yet Purchased, Percent of Equity		(2.25%)	[2],[3]	(1.26%)	[5],[6]
Investments sold short, at fair value-		$ (14,189)	[3]	$ (8,154)	[6]
Proceeds from investments sold short		(14,105)	[3]	(8,052)	[6]
Common Stock Sold Short [Member] | Exchange Traded Equity [Member] | Energy [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Investments sold short, at fair value-	[3]	$ (313)
Investment Sold, Not yet Purchased, Balance, Shares	[3]	(13)
Common Stock Sold Short [Member] | Exchange Traded Equity [Member] | Financial [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Investments sold short, at fair value-		$ (13,876)	[3]	$ (8,154)	[6]
Investment Sold, Not yet Purchased, Balance, Shares		(379)	[3]	(207)	[6]
Corporate Debt Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Investment Sold, Not yet Purchased, Percent of Equity		(11.21%)	[2],[3]	(6.14%)	[5],[6]
Investments sold short, at fair value-		$ (70,567)	[3]	$ (39,572)	[6]
Proceeds from investments sold short		(70,082)	[3]	(39,664)	[6]
Corporate Debt Sold Short [Member] | Various Issuer [Member] | Basic Materials [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount		$ (3,310)	[3]	(8,970)	[6]
Rate	[3]	3.75%
Investments maturity date	[3]	2023-02
Investments sold short, at fair value-		$ (3,365)	[3]	$ (8,717)	[6]
Corporate Debt Sold Short [Member] | Various Issuer [Member] | Basic Materials [Member] | North America [Member] | Minimum [Member]
Investments Sold, Not yet Purchased [Line Items]
Rate	[6]			3.88%
Investments maturity date	[6]			2021-10
Corporate Debt Sold Short [Member] | Various Issuer [Member] | Basic Materials [Member] | North America [Member] | Maximum [Member]
Investments Sold, Not yet Purchased [Line Items]
Rate	[6]			5.13%
Investments maturity date	[6]			2023-03
Corporate Debt Sold Short [Member] | Various Issuer [Member] | Communications [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount		(17,690)	[3]	$ (8,750)	[6]
Investments sold short, at fair value-		$ (17,529)	[3]	$ (8,551)	[6]
Corporate Debt Sold Short [Member] | Various Issuer [Member] | Communications [Member] | North America [Member] | Minimum [Member]
Investments Sold, Not yet Purchased [Line Items]
Rate		4.25%	[3]	5.25%	[6]
Investments maturity date		2021-09	[3]	2021-07	[6]
Corporate Debt Sold Short [Member] | Various Issuer [Member] | Communications [Member] | North America [Member] | Maximum [Member]
Investments Sold, Not yet Purchased [Line Items]
Rate		10.50%	[3]	9.25%	[6]
Investments maturity date		2024-11	[3]	2022-09	[6]
Corporate Debt Sold Short [Member] | Various Issuer [Member] | Consumer [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount		$ (23,600)	[3]	$ (8,930)	[6]
Investments sold short, at fair value-		$ (23,758)	[3]	$ (8,695)	[6]
Corporate Debt Sold Short [Member] | Various Issuer [Member] | Consumer [Member] | North America [Member] | Minimum [Member]
Investments Sold, Not yet Purchased [Line Items]
Rate		2.90%	[3]	3.88%	[6]
Investments maturity date		2019-04	[3]	2022-01	[6]
Corporate Debt Sold Short [Member] | Various Issuer [Member] | Consumer [Member] | North America [Member] | Maximum [Member]
Investments Sold, Not yet Purchased [Line Items]
Rate		7.38%	[3]	6.88%	[6]
Investments maturity date		2026-05	[3]	2026-04	[6]
Corporate Debt Sold Short [Member] | Various Issuer [Member] | Energy [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount		$ (21,490)	[3]	$ (10,597)	[6]
Investments sold short, at fair value-		$ (21,138)	[3]	$ (10,041)	[6]
Corporate Debt Sold Short [Member] | Various Issuer [Member] | Energy [Member] | North America [Member] | Minimum [Member]
Investments Sold, Not yet Purchased [Line Items]
Rate		3.25%	[3]	2.40%	[6]
Investments maturity date		2022-04	[3]	2021-06	[6]
Corporate Debt Sold Short [Member] | Various Issuer [Member] | Energy [Member] | North America [Member] | Maximum [Member]
Investments Sold, Not yet Purchased [Line Items]
Rate		8.00%	[3]	8.00%	[6]
Investments maturity date		2027-06	[3]	2025-01	[6]
Corporate Debt Sold Short [Member] | Various Issuer [Member] | Financial [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount		$ (3,440)	[3]	$ (1,130)	[6]
Rate	[6]			4.13%
Investments maturity date	[6]			2022-02
Investments sold short, at fair value-		$ (3,653)	[3]	$ (1,121)	[6]
Corporate Debt Sold Short [Member] | Various Issuer [Member] | Financial [Member] | North America [Member] | Minimum [Member]
Investments Sold, Not yet Purchased [Line Items]
Rate	[3]	5.13%
Investments maturity date	[3]	2022-03
Corporate Debt Sold Short [Member] | Various Issuer [Member] | Financial [Member] | North America [Member] | Maximum [Member]
Investments Sold, Not yet Purchased [Line Items]
Rate	[3]	5.25%
Investments maturity date	[3]	2024-09
Corporate Debt Sold Short [Member] | Various Issuer [Member] | Technology Sector [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[3]	$ (1,050)
Rate	[3]	6.38%
Investments maturity date	[3]	2023-12
Investments sold short, at fair value-	[3]	$ (1,124)
Corporate Debt Sold Short [Member] | Various Issuer [Member] | Utilities [Member] | North America [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	[6]			$ (2,430)
Rate	[6]			6.25%
Investments maturity date	[6]			2022-07
Investments sold short, at fair value-	[6]			$ (2,447)
Investments Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Investment Sold, Not yet Purchased, Percent of Equity		(107.29%)	[2],[3]	(90.71%)	[5],[6]
Investments sold short, at fair value-		$ (675,650)	[3]	$ (584,896)	[6]
Proceeds from investments sold short		$ (672,506)	[3]	$ (589,429)	[6]

[1] At September 30, 2017, 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 55.62%, 16.98%, and 2.11% 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.

[4] At December 31, 2016, 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 32.67%, 22.21%, and 7.89% of Total Equity, respectively.

[5] Classification percentages are based on Total Equity.

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