Stock Based Compensation - Summary of All Stock Options Outstanding (Detail) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares subject to option, beginning balance	116,000
Shares subject to option, exercised	(6,000)
Shares subject to option, forfeited	(8,000)
Shares subject to option, ending balance	102,000	116,000
Weighted average exercise price per share, beginning balance	$ 28.27
Weighted average exercise price per share, exercised	$ 8.55
Weighted average exercise price per share, forfeited	$ 35.10
Weighted average exercise price per share, ending balance	$ 28.89	$ 28.27
Aggregate intrinsic value, beginning balance	$ 279,150
Aggregate intrinsic value, ending balance	$ 292,730
Weighted average contractual remaining life in years, beginning balance	5 years 8 months 12 days	6 years