Contingencies - Legal Matters (Details)		1 Months Ended	3 Months Ended
	Aug. 12, 2015 USD ($)	Oct. 31, 2015 USD ($)	Mar. 31, 2016 USD ($) item
Contingencies - Legal Matters
Aggregate amount payable	$ 20,300,000
Civil penalty	18,000,000
Disgorgement of trading revenues	2,100,000
Prejudgment interest	$ 250,000
Number of putative class action lawsuits | item			2
Legal and related costs			$ 300,000
Reserve for probable settlement with SEC			$ 2,500,000
Seeking in cash and equity severance
Contingencies - Legal Matters
Loss contingency damages sought value		$ 8,000,000
Punitive damages
Contingencies - Legal Matters
Loss contingency damages sought value		$ 5,000,000