Contingencies - Narrative (Details) - USD ($)					9 Months Ended
	Jan. 27, 2017	Feb. 17, 2015	Feb. 09, 2015	Jan. 27, 2015	Sep. 30, 2016
Loss Contingencies [Line Items]
Minimum estimated range of aggregate loss for legal proceedings					$ 0
Maximum estimated range of aggregate loss for legal proceedings					62,000,000
Auction Rate Securities Committed To Purchase related to settlements with regulators					3,000,000
Auction rate securities, firm purchased and hold					92,000,000
Amount of ARS committed to purchase from clients					25,500,000
Eligible investor subject to future buyback potential additional losses related to valuation adjustments					33,800,000
Eligible Investor Subject To Future Buyback Potential Additional Losses Related To Valuation Adjustments					0
Litigation settlement, expense					$ 10,000,000
SEC [Member]
Loss Contingencies [Line Items]
Litigation settlement, amount				$ 10,000,000
Payments for legal settlements		$ 5,000,000
SEC [Member] | Disgorgement [Member]
Loss Contingencies [Line Items]
Litigation settlement, amount				4,200,000
SEC [Member] | Prejudgment Interest [Member]
Loss Contingencies [Line Items]
Litigation settlement, amount				753,500
SEC [Member] | Civil Penalties [Member]
Loss Contingencies [Line Items]
Litigation settlement, amount				5,100,000
United States Department of the Treasury [Member]
Loss Contingencies [Line Items]
Litigation settlement, amount				$ 10,000,000
Payments for legal settlements			$ 5,000,000
Forecast [Member] | SEC [Member]
Loss Contingencies [Line Items]
Payments for legal settlements	$ 5,000,000