Estimated Fair Value of Options Granted using Black-Scholes Option-Pricing Model with Weighted-Average Assumptions (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Expected life (years)	9 years 6 months 26 days	10 years	8 years 8 months 12 days	9 years 1 month 10 days
Interest rate	2.10%	1.60%	1.80%	1.50%
Volatility	46.90%	53.40%	47.60%	53.00%
Dividend yield