Derivative Financial Instruments - Remaining Contract Maturity of Fair Value of OTC Derivative Assets and Liabilities (Detail) $ in Thousands	May 31, 2018 USD ($)
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	$ 130,539
OTC derivative assets having maturity period of 1 to 5 years	148,791
OTC derivative assets having maturity period of greater than 5 years	91,617
OTC derivative assets cross-maturity netting	(91,503)
Total OTC derivative assets, net of cross-maturity netting	279,444
Cross product counterparty netting	(34,466)
Total OTC derivative assets included in Financial instruments owned	244,978
OTC derivative liabilities having maturity period of 0 to 12 months	173,291
OTC derivative liabilities having maturity period of 1 to 5 years	326,375
OTC derivative liabilities having maturity period of greater than 5 years	219,038
OTC derivative liabilities cross-maturity netting	(91,503)
Total OTC derivative liabilities, net of cross-maturity netting	627,201
Cross product counterparty netting	(34,466)
Total OTC derivative liabilities included in Financial instruments sold, not yet purchased	592,735
Exchange traded derivative assets	166,000
Cash collateral received	135,600
Exchange traded derivative liabilities, with fair value	126,900
Cash collateral pledged	272,000
Equity swaps and options
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	940
OTC derivative assets having maturity period of 1 to 5 years	4,178
OTC derivative assets having maturity period of greater than 5 years	0
OTC derivative assets cross-maturity netting	(214)
Total OTC derivative assets, net of cross-maturity netting	4,904
OTC derivative liabilities having maturity period of 0 to 12 months	13,752
OTC derivative liabilities having maturity period of 1 to 5 years	69,159
OTC derivative liabilities having maturity period of greater than 5 years	3,141
OTC derivative liabilities cross-maturity netting	(214)
Total OTC derivative liabilities, net of cross-maturity netting	85,838
Credit default swaps
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	26
OTC derivative assets having maturity period of 1 to 5 years	20,045
OTC derivative assets having maturity period of greater than 5 years	2,790
OTC derivative assets cross-maturity netting	(779)
Total OTC derivative assets, net of cross-maturity netting	22,082
OTC derivative liabilities having maturity period of 0 to 12 months	64
OTC derivative liabilities having maturity period of 1 to 5 years	7,405
OTC derivative liabilities having maturity period of greater than 5 years	6
OTC derivative liabilities cross-maturity netting	(779)
Total OTC derivative liabilities, net of cross-maturity netting	6,696
Total return swaps
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	49,176
OTC derivative assets having maturity period of 1 to 5 years	3,233
OTC derivative assets having maturity period of greater than 5 years	0
OTC derivative assets cross-maturity netting	(756)
Total OTC derivative assets, net of cross-maturity netting	51,653
OTC derivative liabilities having maturity period of 0 to 12 months	64,750
OTC derivative liabilities having maturity period of 1 to 5 years	101,271
OTC derivative liabilities having maturity period of greater than 5 years	0
OTC derivative liabilities cross-maturity netting	(756)
Total OTC derivative liabilities, net of cross-maturity netting	165,265
Foreign currency forwards, swaps and options
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	58,321
OTC derivative assets having maturity period of 1 to 5 years	17,215
OTC derivative assets having maturity period of greater than 5 years	0
OTC derivative assets cross-maturity netting	(3,355)
Total OTC derivative assets, net of cross-maturity netting	72,181
OTC derivative liabilities having maturity period of 0 to 12 months	55,185
OTC derivative liabilities having maturity period of 1 to 5 years	13,123
OTC derivative liabilities having maturity period of greater than 5 years	0
OTC derivative liabilities cross-maturity netting	(3,355)
Total OTC derivative liabilities, net of cross-maturity netting	64,953
Fixed income forwards
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	477
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	477
OTC derivative liabilities having maturity period of 0 to 12 months	3,879
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	3,879
Interest rate swaps, options and forwards
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	21,599
OTC derivative assets having maturity period of 1 to 5 years	104,120
OTC derivative assets having maturity period of greater than 5 years	88,827
OTC derivative assets cross-maturity netting	(86,399)
Total OTC derivative assets, net of cross-maturity netting	128,147
OTC derivative liabilities having maturity period of 0 to 12 months	35,661
OTC derivative liabilities having maturity period of 1 to 5 years	135,417
OTC derivative liabilities having maturity period of greater than 5 years	215,891
OTC derivative liabilities cross-maturity netting	(86,399)
Total OTC derivative liabilities, net of cross-maturity netting	$ 300,570