Derivative Financial Instruments - Remaining Contract Maturity of Fair Value of OTC Derivative Assets and Liabilities (Detail) $ in Thousands	Aug. 31, 2016 USD ($)
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	$ 182,196
OTC derivative assets having maturity period of 1 to 5 years	274,079
OTC derivative assets having maturity period of greater than 5 years	88,435
OTC derivative assets cross-maturity netting	(105,015)
Total OTC derivative assets, net of cross-maturity netting	439,695
Cross product counterparty netting	(754)
Total OTC derivative assets included in Financial instruments owned	438,941
OTC derivative liabilities having maturity period of 0 to 12 months	181,712
OTC derivative liabilities having maturity period of 1 to 5 years	192,922
OTC derivative liabilities having maturity period of greater than 5 years	126,213
OTC derivative liabilities cross-maturity netting	(105,015)
Total OTC derivative liabilities, net of cross-maturity netting	395,832
Cross product counterparty netting	(754)
Total OTC derivative liabilities included in Financial instruments sold, not yet purchased	395,078
Equity Swaps And Options [Member]
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	27,781
OTC derivative assets having maturity period of 1 to 5 years	5,370
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	33,151
OTC derivative liabilities having maturity period of 0 to 12 months	13,408
OTC derivative liabilities having maturity period of 1 to 5 years	23,617
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	37,025
Credit Default Swap [Member]
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	0
OTC derivative assets having maturity period of 1 to 5 years	7,948
OTC derivative assets having maturity period of greater than 5 years	230
OTC derivative assets cross-maturity netting	(177)
Total OTC derivative assets, net of cross-maturity netting	8,001
OTC derivative liabilities having maturity period of 0 to 12 months	28
OTC derivative liabilities having maturity period of 1 to 5 years	12,639
OTC derivative liabilities having maturity period of greater than 5 years	1,672
OTC derivative liabilities cross-maturity netting	(177)
Total OTC derivative liabilities, net of cross-maturity netting	14,162
Total Return Swap [Member]
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	27,796
OTC derivative assets having maturity period of 1 to 5 years	874
OTC derivative assets having maturity period of greater than 5 years	0
OTC derivative assets cross-maturity netting	(613)
Total OTC derivative assets, net of cross-maturity netting	28,057
OTC derivative liabilities having maturity period of 0 to 12 months	26,824
OTC derivative liabilities having maturity period of 1 to 5 years	16,967
OTC derivative liabilities having maturity period of greater than 5 years	0
OTC derivative liabilities cross-maturity netting	(613)
Total OTC derivative liabilities, net of cross-maturity netting	43,178
Foreign Currency Forwards Swaps And Options [Member]
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	84,564
OTC derivative assets having maturity period of 1 to 5 years	29,937
OTC derivative assets having maturity period of greater than 5 years	0
OTC derivative assets cross-maturity netting	(7,150)
Total OTC derivative assets, net of cross-maturity netting	107,351
OTC derivative liabilities having maturity period of 0 to 12 months	112,699
OTC derivative liabilities having maturity period of 1 to 5 years	20,024
OTC derivative liabilities having maturity period of greater than 5 years	0
OTC derivative liabilities cross-maturity netting	(7,150)
Total OTC derivative liabilities, net of cross-maturity netting	125,573
Fixed Income Forwards [Member]
Derivative [Line Items]
OTC derivative liabilities having maturity period of 0 to 12 months	5,044
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	5,044
Interest Rate Swaps, Options and Forwards [Member]
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	42,055
OTC derivative assets having maturity period of 1 to 5 years	229,950
OTC derivative assets having maturity period of greater than 5 years	88,205
OTC derivative assets cross-maturity netting	(97,075)
Total OTC derivative assets, net of cross-maturity netting	263,135
OTC derivative liabilities having maturity period of 0 to 12 months	23,709
OTC derivative liabilities having maturity period of 1 to 5 years	119,675
OTC derivative liabilities having maturity period of greater than 5 years	124,541
OTC derivative liabilities cross-maturity netting	(97,075)
Total OTC derivative liabilities, net of cross-maturity netting	$ 170,850