Derivative Financial Instruments - Remaining Contract Maturity of Fair Value of OTC Derivative Assets and Liabilities (Detail) $ in Thousands	May 31, 2017 USD ($)
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	$ 132,095
OTC derivative assets having maturity period of 1 to 5 years	178,926
OTC derivative assets having maturity period of greater than 5 years	107,695
OTC derivative assets cross-maturity netting	(69,553)
Total OTC derivative assets, net of cross-maturity netting	349,163
Cross product counterparty netting	(11,429)
Total OTC derivative assets included in Financial instruments owned	337,734
OTC derivative liabilities having maturity period of 0 to 12 months	139,948
OTC derivative liabilities having maturity period of 1 to 5 years	129,894
OTC derivative liabilities having maturity period of greater than 5 years	91,746
OTC derivative liabilities cross-maturity netting	(69,553)
Total OTC derivative liabilities, net of cross-maturity netting	292,035
Cross product counterparty netting	(11,429)
Total OTC derivative liabilities included in Financial instruments sold, not yet purchased	280,606
Equity swaps and options [Member]
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	4,049
OTC derivative assets having maturity period of 1 to 5 years	3,451
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	7,500
OTC derivative liabilities having maturity period of 0 to 12 months	13,419
OTC derivative liabilities having maturity period of 1 to 5 years	17,600
OTC derivative liabilities having maturity period of greater than 5 years	2,385
OTC derivative liabilities cross-maturity netting	0
Total OTC derivative liabilities, net of cross-maturity netting	33,404
Credit default swaps [Member]
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	3,671
OTC derivative assets having maturity period of 1 to 5 years	1,515
OTC derivative assets having maturity period of greater than 5 years	3,862
OTC derivative assets cross-maturity netting	(164)
Total OTC derivative assets, net of cross-maturity netting	8,884
OTC derivative liabilities having maturity period of 0 to 12 months	1,986
OTC derivative liabilities having maturity period of 1 to 5 years	12,843
OTC derivative liabilities having maturity period of greater than 5 years	2,651
OTC derivative liabilities cross-maturity netting	(164)
Total OTC derivative liabilities, net of cross-maturity netting	17,316
Total return swap [Member]
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	20,455
OTC derivative assets having maturity period of 1 to 5 years	2,652
OTC derivative assets having maturity period of greater than 5 years	262
OTC derivative assets cross-maturity netting	(822)
Total OTC derivative assets, net of cross-maturity netting	22,547
OTC derivative liabilities having maturity period of 0 to 12 months	18,801
OTC derivative liabilities having maturity period of 1 to 5 years	4,075
OTC derivative liabilities having maturity period of greater than 5 years	203
OTC derivative liabilities cross-maturity netting	(822)
Total OTC derivative liabilities, net of cross-maturity netting	22,257
Foreign currency forwards swaps and options [Member]
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	67,838
OTC derivative assets having maturity period of 1 to 5 years	6,873
OTC derivative assets having maturity period of greater than 5 years	0
OTC derivative assets cross-maturity netting	(2,998)
Total OTC derivative assets, net of cross-maturity netting	71,713
OTC derivative liabilities having maturity period of 0 to 12 months	70,074
OTC derivative liabilities having maturity period of 1 to 5 years	3,065
OTC derivative liabilities having maturity period of greater than 5 years	0
OTC derivative liabilities cross-maturity netting	(2,998)
Total OTC derivative liabilities, net of cross-maturity netting	70,141
Fixed income forwards [Member]
Derivative [Line Items]
OTC derivative liabilities having maturity period of 0 to 12 months	1,687
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	1,687
Interest rate swaps, options and forwards [Member]
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	36,082
OTC derivative assets having maturity period of 1 to 5 years	164,435
OTC derivative assets having maturity period of greater than 5 years	103,571
OTC derivative assets cross-maturity netting	(65,569)
Total OTC derivative assets, net of cross-maturity netting	238,519
OTC derivative liabilities having maturity period of 0 to 12 months	33,981
OTC derivative liabilities having maturity period of 1 to 5 years	92,311
OTC derivative liabilities having maturity period of greater than 5 years	86,507
OTC derivative liabilities cross-maturity netting	(65,569)
Total OTC derivative liabilities, net of cross-maturity netting	$ 147,230