Derivative Financial Instruments - Remaining Contract Maturity of Fair Value of OTC Derivative Assets and Liabilities (Detail) $ in Thousands	Aug. 31, 2015 USD ($)
Remaining Contract Maturity Of Fair Value Of Over Counter Derivative Assets And Liabilities [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	$ 301,613
OTC derivative assets having maturity period of 1 to 5 years	193,330
OTC derivative assets having maturity period of greater than 5 years	95,844
OTC derivative assets cross-maturity netting	(47,857)
Total OTC derivative assets, net of cross-maturity netting	542,930
Cross product counterparty netting	(10,029)
Total OTC derivative assets included in Financial instruments owned	532,901
OTC derivative liabilities having maturity period of 0 to 12 months	279,322
OTC derivative liabilities having maturity period of 1 to 5 years	177,212
OTC derivative liabilities having maturity period of greater than 5 years	113,202
OTC derivative liabilities cross-maturity netting	(47,857)
Total OTC derivative liabilities, net of cross-maturity netting	521,879
Cross product counterparty netting	(10,029)
Total OTC derivative liabilities included in Financial instruments sold, not yet purchased	511,850
Commodity swaps, options and forwards [Member]
Remaining Contract Maturity Of Fair Value Of Over Counter Derivative Assets And Liabilities [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	9,025
OTC derivative assets having maturity period of 1 to 5 years	1,112
OTC derivative assets having maturity period of greater than 5 years	14,037
OTC derivative assets cross-maturity netting	0
Total OTC derivative assets, net of cross-maturity netting	24,174
OTC derivative liabilities having maturity period of 0 to 12 months	2,959
OTC derivative liabilities having maturity period of 1 to 5 years	0
OTC derivative liabilities having maturity period of greater than 5 years	5,470
OTC derivative liabilities cross-maturity netting	0
Total OTC derivative liabilities, net of cross-maturity netting	8,429
Equity swaps and options [Member]
Remaining Contract Maturity Of Fair Value Of Over Counter Derivative Assets And Liabilities [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	33,975
OTC derivative assets having maturity period of 1 to 5 years	8,486
OTC derivative assets having maturity period of greater than 5 years	2,316
OTC derivative assets cross-maturity netting	0
Total OTC derivative assets, net of cross-maturity netting	44,777
OTC derivative liabilities having maturity period of 0 to 12 months	16,909
OTC derivative liabilities having maturity period of 1 to 5 years	39,538
OTC derivative liabilities having maturity period of greater than 5 years	9,139
OTC derivative liabilities cross-maturity netting	0
Total OTC derivative liabilities, net of cross-maturity netting	65,586
Credit default swaps [Member]
Remaining Contract Maturity Of Fair Value Of Over Counter Derivative Assets And Liabilities [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	54
OTC derivative assets having maturity period of 1 to 5 years	4,084
OTC derivative assets having maturity period of greater than 5 years	2,224
OTC derivative assets cross-maturity netting	(1,832)
Total OTC derivative assets, net of cross-maturity netting	4,530
OTC derivative liabilities having maturity period of 0 to 12 months	0
OTC derivative liabilities having maturity period of 1 to 5 years	1,519
OTC derivative liabilities having maturity period of greater than 5 years	11,016
OTC derivative liabilities cross-maturity netting	(1,832)
Total OTC derivative liabilities, net of cross-maturity netting	10,703
Total return swaps [Member]
Remaining Contract Maturity Of Fair Value Of Over Counter Derivative Assets And Liabilities [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	23,005
OTC derivative assets having maturity period of 1 to 5 years	4
OTC derivative assets having maturity period of greater than 5 years	0
OTC derivative assets cross-maturity netting	(180)
Total OTC derivative assets, net of cross-maturity netting	22,829
OTC derivative liabilities having maturity period of 0 to 12 months	54,507
OTC derivative liabilities having maturity period of 1 to 5 years	1,927
OTC derivative liabilities having maturity period of greater than 5 years	1,967
OTC derivative liabilities cross-maturity netting	(180)
Total OTC derivative liabilities, net of cross-maturity netting	58,221
Foreign currency forwards, swaps and options [Member]
Remaining Contract Maturity Of Fair Value Of Over Counter Derivative Assets And Liabilities [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	165,529
OTC derivative assets having maturity period of 1 to 5 years	21,372
OTC derivative assets having maturity period of greater than 5 years	0
OTC derivative assets cross-maturity netting	(11,252)
Total OTC derivative assets, net of cross-maturity netting	175,649
OTC derivative liabilities having maturity period of 0 to 12 months	157,468
OTC derivative liabilities having maturity period of 1 to 5 years	48,147
OTC derivative liabilities having maturity period of greater than 5 years	0
OTC derivative liabilities cross-maturity netting	(11,252)
Total OTC derivative liabilities, net of cross-maturity netting	194,363
Fixed income forwards [Member]
Remaining Contract Maturity Of Fair Value Of Over Counter Derivative Assets And Liabilities [Line Items]
OTC derivative liabilities having maturity period of 0 to 12 months	342
OTC derivative liabilities having maturity period of 1 to 5 years	0
OTC derivative liabilities having maturity period of greater than 5 years	0
OTC derivative liabilities cross-maturity netting	0
Total OTC derivative liabilities, net of cross-maturity netting	342
Interest rate swaps, options and forwards [Member]
Remaining Contract Maturity Of Fair Value Of Over Counter Derivative Assets And Liabilities [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	70,025
OTC derivative assets having maturity period of 1 to 5 years	158,272
OTC derivative assets having maturity period of greater than 5 years	77,267
OTC derivative assets cross-maturity netting	(34,593)
Total OTC derivative assets, net of cross-maturity netting	270,971
OTC derivative liabilities having maturity period of 0 to 12 months	47,137
OTC derivative liabilities having maturity period of 1 to 5 years	86,081
OTC derivative liabilities having maturity period of greater than 5 years	85,610
OTC derivative liabilities cross-maturity netting	(34,593)
Total OTC derivative liabilities, net of cross-maturity netting	$ 184,235