Commitments and Contingencies - Legal Matters (Details)	1 Months Ended		3 Months Ended	12 Months Ended
	Oct. 31, 2015 USD ($)	Aug. 31, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) item
Contingencies - Legal Matters
Number of putative class action lawsuits | item				2
Aggregate amount payable		$ 20,300,000	$ 20,300,000
Civil penalty		18,000,000
Disgorgement of trading revenues		2,100,000
Prejudgment interest		$ 250,000
Reserve for probable settlement with SEC			20,300,000
Legal and related costs			$ 2,300,000	$ 4,900,000
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