Derivative Instruments and Hedging Activities (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Ria Operations [Member] | Foreign Exchange Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Asset, Notional Amount	$ 213.0
Corporate Operations [Member] | Foreign Exchange Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Asset, Notional Amount	193.0
HiFX Operations [Member] | Foreign Exchange Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Asset, Notional Amount	$ 1,500.0
Maximum [Member] | Ria Operations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Foreign currency forward contract term	14 days
Trading Revenue [Member] | HiFX Operations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Foreign Currency Exchange Margin	$ 18.1	$ 18.6