Contingencies - Legal Matters (Details)	3 Months Ended
	Jun. 30, 2015 USD ($)
Contingencies - Legal Matters
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