Derivatives, Derivatives Instruments Gain (Loss) in Income Statement (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2020		Sep. 30, 2019		Sep. 30, 2020		Sep. 30, 2019
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	$ 8,174		$ 8,314		$ 9,560		$ 21,070
Gain (Loss) on Derivatives, Net	2,354		3,778		42,659		19,595
Total customer risk management programs
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	8,642		4,684		18,106		16,705
Gain (Loss) on Derivatives, Net	0		0		0		0
To-be-announced residential mortgage-backed securities [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	0		1,667		0		9,579
Gain (Loss) on Derivatives, Net	0		0		0		0
Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	1,014		1,252		2,702		2,787
Gain (Loss) on Derivatives, Net	0		0		0		0
Energy contracts [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	7,460		1,611		14,850		3,923
Gain (Loss) on Derivatives, Net	0		0		0		0
Agricultural contracts [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	6		16		27		24
Gain (Loss) on Derivatives, Net	0		0		0		0
Foreign exchange contracts [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	162		138		527		392
Gain (Loss) on Derivatives, Net	0		0		0		0
Equity option contracts [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	0		0		0		0
Gain (Loss) on Derivatives, Net	0		0		0		0
Trading [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	(468)	[1]	3,630	[1]	(8,546)	[2]	4,365	[2]
Gain (Loss) on Derivatives, Net	0	[1]	0	[1]	0	[2]	0	[2]
Internal risk management programs [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	0		0		0		0
Gain (Loss) on Derivatives, Net	$ 2,354		$ 3,778		$ 42,659		$ 19,595

[1] Represents changes in fair value of to-be-announced securities and other derivative instruments held to mitigate market risk of trading securities portfolio, which is offset by changes in fair value of trading securities also include in Brokerage and Trading Revenue in the Consolidated Statements of Earnings.

[2] Represents changes in fair value of to-be-announced securities and other derivative instruments held to mitigate market risk of trading securities portfolio, which is offset by changes in fair value of trading securities also include in Brokerage and Trading Revenue in the Consolidated Statements of Earnings.