Derivatives, Derivatives Instruments Gain (Loss) in Income Statement (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	$ 25,192	$ 48,761	$ 42,603
Gain (Loss) on Derivatives, Net	(422)	779	(15,685)
To-be-announced residential mortgage-backed securities [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	27,190	34,532	38,523
Gain (Loss) on Derivatives, Net	0	0	0
Interest rate swaps [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	2,614	2,647	2,589
Gain (Loss) on Derivatives, Net	0	0	0
Energy contracts [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	8,443	5,536	5,027
Gain (Loss) on Derivatives, Net	0	0	0
Agricultural contracts [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	53	79	111
Gain (Loss) on Derivatives, Net	0	0	0
Foreign exchange contracts [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	535	1,352	945
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	38,835	44,146	47,195
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	(13,643)	4,615	(4,592)
Gain (Loss) on Derivatives, Net	$ (422)	$ 779	$ (15,685)