Derivatives, Derivatives Instruments Gain (Loss) in Income Statement (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	$ 32,940	$ 25,192	$ 48,761
Gain (Loss) on Derivatives, Net	14,951	(422)	779
To-be-announced residential mortgage-backed securities [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	9,579	27,190	34,532
Gain (Loss) on Derivatives, Net	0	0	0
Interest rate swaps [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	3,647	2,614	2,647
Gain (Loss) on Derivatives, Net	0	0	0
Energy contracts [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	5,064	8,443	5,536
Gain (Loss) on Derivatives, Net	0	0	0
Agricultural contracts [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	28	53	79
Gain (Loss) on Derivatives, Net	0	0	0
Foreign exchange contracts [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	623	535	1,352
Gain (Loss) on Derivatives, Net	0	0	0
Equity option contracts [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	0	0	0
Gain (Loss) on Derivatives, Net	0	0	0
Total customer risk management programs [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	18,941	38,835	44,146
Gain (Loss) on Derivatives, Net	0	0	0
Trading [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	13,999	(13,643)	4,615
Gain (Loss) on Derivatives, Net	0	0	0
Internal risk management programs [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	0	0	0
Gain (Loss) on Derivatives, Net	$ 14,951	$ (422)	$ 779