Contingencies - Legal Matters (Details) $ in Thousands			3 Months Ended
	Jan. 12, 2017 USD ($)	Aug. 12, 2015 USD ($) item	Mar. 31, 2017	Dec. 31, 2016 USD ($)
Contingencies – Legal Matters
Accrued settlement costs				$ 24,450
Settlement with S E C for Investigation into Proprietary Trading Pilot
Contingencies – Legal Matters
Number of putative class action lawsuits | item		2
Number of days for plaintiff to file a motion to amend its complaint			30 days
Settlement Agreement With SEC Involving Prereleased ADRs
Contingencies – Legal Matters
Payment of settlement amount	$ 24,500
Civil penalty	7,500
Disgorgement payment	15,100
Prejudgment interest	$ 1,900
Accrued settlement costs				$ 24,500
Settlement with S E C for Investigation into Proprietary Trading Pilot
Contingencies – Legal Matters
Payment of settlement amount		$ 20,300
Civil penalty		18,000
Disgorgement payment		2,100
Prejudgment interest		$ 250