Fair Value-Based Measurements and Weighted-Average Assumptions (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average fair value	$ 1.57	$ 2.70
Risk-free interest rate	1.80%	1.10%
Expected life (in years)	5 years 10 months 24 days	5 years 9 months 18 days
Volatility	1.40%	1.40%
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average fair value	$ 0.92	$ 1.46
Risk-free interest rate	0.20%	0.20%
Expected life (in years)	1 year 1 month 6 days	1 year 3 months 18 days
Volatility	0.90%	0.70%