Contingencies - Additional Information (Detail) (USD $)	6 Months Ended
	Jun. 30, 2014
Commitments and Contingencies Disclosure [Abstract]
Minimum estimated range of aggregate loss for legal proceedings	$ 0
Maximum estimated range of aggregate loss for legal proceedings	30,000,000
Total amount of ARS the firm purchased and hold	99,400,000
Amount of ARS committed to purchase from clients	20,200,000
Eligible investor subject to future buyback potential additional losses related to valuation adjustments	$ 110,600,000
Period of auction rates security to be purchased from rendering of the award	30 days