Contingencies - Legal Matters (Details)				9 Months Ended
	Jan. 12, 2017 USD ($)	Nov. 27, 2015 item	Aug. 12, 2015 USD ($) item	Sep. 30, 2017 USD ($) item	Dec. 31, 2016 USD ($)
Contingencies – Legal Matters
Accrued settlement costs				$ 0	$ 24,450,000
Minimum
Contingencies – Legal Matters
Number of lawsuits proceedings may have a material impact on the results of operations for any particular period | item				1
Settlement with S E C for Investigation into Proprietary Trading Pilot
Contingencies – Legal Matters
Number of putative class action lawsuits | item			2
Settlement Agreement With SEC Involving Prereleased ADRs
Contingencies – Legal Matters
Payment of settlement amount	$ 24,500,000
Civil penalty	7,500,000
Disgorgement payment	15,100,000
Prejudgment interest	$ 1,900,000
Accrued settlement costs					$ 24,500,000
Settlement with S E C for Investigation into Proprietary Trading Pilot
Contingencies – Legal Matters
Payment of settlement amount			$ 20,300,000
Civil penalty			18,000,000
Disgorgement payment			2,100,000
Prejudgment interest			$ 250,000
Case of derivative action captioned Watterson v. Gasser et al.
Contingencies – Legal Matters
Number of current or former officers and directors of the company got filed by the company | item		11