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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	$ 8,314	$ 14,639	$ 21,070	$ 32,477
Gain (Loss) on Derivatives, Net	3,778	(2,847)	19,595	(11,589)
To-be-announced residential mortgage-backed securities [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	1,667	7,272	9,579	21,677
Gain (Loss) on Derivatives, Net	0	0	0	0
Interest rate swaps [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	1,252	618	2,787	2,057
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	1,611	541	3,923	5,097
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	16	6	24	36
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	138	78	392	350
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
Total customer risk management programs
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	4,684	8,515	16,705	29,217
Gain (Loss) on Derivatives, Net	0	0	0	0
Trading [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	3,630	6,124	4,365	3,260
Gain (Loss) on Derivatives, Net	0	0	0	0
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	$ 3,778	$ (2,847)	$ 19,595	$ (11,589)