Derivative Financial Instruments - Remaining Contract Maturity of Fair Value of OTC Derivative Assets and Liabilities (Details) $ in Thousands	Aug. 31, 2019 USD ($)
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	$ 271,599
OTC derivative assets having maturity period of 1 to 5 years	301,036
OTC derivative assets having maturity period of greater than 5 years	187,323
OTC derivative assets cross-maturity netting	(64,292)
Total OTC derivative assets, net of cross-maturity netting	695,666
Cross product counterparty netting	(26,934)
Total OTC derivative assets included in Financial instruments owned	668,732
OTC derivative liabilities having maturity period of 0 to 12 months	237,524
OTC derivative liabilities having maturity period of 1 to 5 years	201,224
OTC derivative liabilities having maturity period of greater than 5 years	162,421
OTC derivative liabilities cross-maturity netting	(64,292)
Total OTC derivative liabilities, net of cross-maturity netting	536,877
Cross product counterparty netting	(26,934)
Total OTC derivative liabilities included in Financial instruments sold, not yet purchased	509,943
Exchange traded derivative assets, with fair value	30,300
Cash collateral received	213,200
Exchange traded derivative liabilities, with fair value	370,800
Cash collateral pledged	318,000
Equity swaps and options
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	57,345
OTC derivative assets having maturity period of 1 to 5 years	1
OTC derivative assets having maturity period of greater than 5 years	3,579
OTC derivative assets cross-maturity netting	(3,572)
Total OTC derivative assets, net of cross-maturity netting	57,353
OTC derivative liabilities having maturity period of 0 to 12 months	8,679
OTC derivative liabilities having maturity period of 1 to 5 years	123,854
OTC derivative liabilities having maturity period of greater than 5 years	49,873
OTC derivative liabilities cross-maturity netting	(3,572)
Total OTC derivative liabilities, net of cross-maturity netting	178,834
Credit default swaps
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	887
OTC derivative assets having maturity period of 1 to 5 years	826
OTC derivative assets having maturity period of greater than 5 years	0
OTC derivative assets cross-maturity netting	(81)
Total OTC derivative assets, net of cross-maturity netting	1,632
OTC derivative liabilities having maturity period of 0 to 12 months	35
OTC derivative liabilities having maturity period of 1 to 5 years	6,291
OTC derivative liabilities having maturity period of greater than 5 years	0
OTC derivative liabilities cross-maturity netting	(81)
Total OTC derivative liabilities, net of cross-maturity netting	6,245
Total return swaps
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	25,166
OTC derivative assets having maturity period of 1 to 5 years	70,022
OTC derivative assets having maturity period of greater than 5 years	0
OTC derivative assets cross-maturity netting	(334)
Total OTC derivative assets, net of cross-maturity netting	94,854
OTC derivative liabilities having maturity period of 0 to 12 months	77,259
OTC derivative liabilities having maturity period of 1 to 5 years	25,160
OTC derivative liabilities having maturity period of greater than 5 years	0
OTC derivative liabilities cross-maturity netting	(334)
Total OTC derivative liabilities, net of cross-maturity netting	102,085
Foreign currency forwards, swaps and options
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	111,325
OTC derivative assets having maturity period of 1 to 5 years	4,740
OTC derivative assets having maturity period of greater than 5 years	7
OTC derivative assets cross-maturity netting	(3,538)
Total OTC derivative assets, net of cross-maturity netting	112,534
OTC derivative liabilities having maturity period of 0 to 12 months	108,267
OTC derivative liabilities having maturity period of 1 to 5 years	2,758
OTC derivative liabilities having maturity period of greater than 5 years	2,984
OTC derivative liabilities cross-maturity netting	(3,538)
Total OTC derivative liabilities, net of cross-maturity netting	110,471
Fixed income forwards
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	556
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	556
OTC derivative liabilities having maturity period of 0 to 12 months	868
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	868
Interest rate swaps, options and forwards
Derivative [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	76,320
OTC derivative assets having maturity period of 1 to 5 years	225,447
OTC derivative assets having maturity period of greater than 5 years	183,737
OTC derivative assets cross-maturity netting	(56,767)
Total OTC derivative assets, net of cross-maturity netting	428,737
OTC derivative liabilities having maturity period of 0 to 12 months	42,416
OTC derivative liabilities having maturity period of 1 to 5 years	43,161
OTC derivative liabilities having maturity period of greater than 5 years	109,564
OTC derivative liabilities cross-maturity netting	(56,767)
Total OTC derivative liabilities, net of cross-maturity netting	$ 138,374