Derivative Instruments and Hedging Activities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Ria Operations [Member] | Foreign Exchange Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	$ 328,000		$ 328,000
Corporate Operations [Member] | Foreign Exchange Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	275,000		275,000
HiFX Operations [Member] | Foreign Exchange Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	1,200,000		$ 1,200,000
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	$ 16,800	$ 16,700	$ 52,500	$ 48,400