Regulatory Requirements - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Regulatory Capital Requirements [Abstract]
Minimum net capital requirements	$ 5,000
Net capital	7,400,000	7,200,000
Excess net capital	$ 6,600,000	$ 6,300,000
Aggregate indebtedness to net capital ratio	1.62	1.85
Description of minimum net capital requirements	The greater of $5,000 or 1/15 of aggregate indebtedness