Derivative Financial Instruments - Remaining Contract Maturity of Fair Value of OTC Derivative Assets and Liabilities (Detail) $ in Thousands	Aug. 31, 2017 USD ($)
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	$ 140,577
OTC derivative assets having maturity period of 1 to 5 years	183,747
OTC derivative assets having maturity period of greater than 5 years	98,719
OTC derivative assets cross-maturity netting	(86,459)
Total OTC derivative assets, net of cross-maturity netting	336,584
Cross product counterparty netting	(19,647)
Total OTC derivative assets included in Financial instruments owned	316,937
OTC derivative liabilities having maturity period of 0 to 12 months	119,891
OTC derivative liabilities having maturity period of 1 to 5 years	270,909
OTC derivative liabilities having maturity period of greater than 5 years	105,100
OTC derivative liabilities cross-maturity netting	(86,459)
Total OTC derivative liabilities, net of cross-maturity netting	409,441
Cross product counterparty netting	(19,647)
Total OTC derivative liabilities included in Financial instruments sold, not yet purchased	389,794
Exchange traded derivative assets	13,400
Cash collateral received	157,300
Exchange traded derivative liabilities, with fair value	429,900
Cash collateral pledged	276,000
Equity swaps and options
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	5,117
OTC derivative assets having maturity period of 1 to 5 years	2,703
OTC derivative assets having maturity period of greater than 5 years	0
OTC derivative assets cross-maturity netting	0
Total OTC derivative assets, net of cross-maturity netting	7,820
OTC derivative liabilities having maturity period of 0 to 12 months	2,980
OTC derivative liabilities having maturity period of 1 to 5 years	146,317
OTC derivative liabilities having maturity period of greater than 5 years	2,534
OTC derivative liabilities cross-maturity netting	0
Total OTC derivative liabilities, net of cross-maturity netting	151,831
Credit default swaps
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	289
OTC derivative assets having maturity period of 1 to 5 years	3,399
OTC derivative assets having maturity period of greater than 5 years	0
OTC derivative assets cross-maturity netting	(26)
Total OTC derivative assets, net of cross-maturity netting	3,662
OTC derivative liabilities having maturity period of 0 to 12 months	1,077
OTC derivative liabilities having maturity period of 1 to 5 years	23,931
OTC derivative liabilities having maturity period of greater than 5 years	0
OTC derivative liabilities cross-maturity netting	(26)
Total OTC derivative liabilities, net of cross-maturity netting	24,982
Total return swaps
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	11,411
OTC derivative assets having maturity period of 1 to 5 years	5,823
OTC derivative assets having maturity period of greater than 5 years	0
OTC derivative assets cross-maturity netting	(2,458)
Total OTC derivative assets, net of cross-maturity netting	14,776
OTC derivative liabilities having maturity period of 0 to 12 months	11,666
OTC derivative liabilities having maturity period of 1 to 5 years	1,802
OTC derivative liabilities having maturity period of greater than 5 years	0
OTC derivative liabilities cross-maturity netting	(2,458)
Total OTC derivative liabilities, net of cross-maturity netting	11,010
Foreign currency forwards, swaps and options
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	73,912
OTC derivative assets having maturity period of 1 to 5 years	131
OTC derivative assets having maturity period of greater than 5 years	0
OTC derivative assets cross-maturity netting	(14)
Total OTC derivative assets, net of cross-maturity netting	74,029
OTC derivative liabilities having maturity period of 0 to 12 months	72,288
OTC derivative liabilities having maturity period of 1 to 5 years	1,575
OTC derivative liabilities having maturity period of greater than 5 years	0
OTC derivative liabilities cross-maturity netting	(14)
Total OTC derivative liabilities, net of cross-maturity netting	73,849
Fixed income forwards
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	134
OTC derivative assets having maturity period of 1 to 5 years	0
OTC derivative assets having maturity period of greater than 5 years	0
OTC derivative assets cross-maturity netting	0
Total OTC derivative assets, net of cross-maturity netting	134
OTC derivative liabilities having maturity period of 0 to 12 months	1,145
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	1,145
Interest rate swaps, options and forwards
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	49,714
OTC derivative assets having maturity period of 1 to 5 years	171,691
OTC derivative assets having maturity period of greater than 5 years	98,719
OTC derivative assets cross-maturity netting	(83,961)
Total OTC derivative assets, net of cross-maturity netting	236,163
OTC derivative liabilities having maturity period of 0 to 12 months	30,735
OTC derivative liabilities having maturity period of 1 to 5 years	97,284
OTC derivative liabilities having maturity period of greater than 5 years	102,566
OTC derivative liabilities cross-maturity netting	(83,961)
Total OTC derivative liabilities, net of cross-maturity netting	$ 146,624