Stock-Based Compensation - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Plan with maximum term from the date of grant	10 years
Percentage of discount on purchase price of share with fair market value	15.00%
ESPP generally provides offering periods	6 months
Initial offering period under the ESPP	May 15 and November 15
Percentage of purchase price of share with fair market value	85.00%
Stock-based compensation expense	$ 865,000	$ 850,000
Options granted become exercisable ratably over the vesting period	5 years
Weighted-average grant date fair value of options granted	$ 24.74
Total unrecognized compensation expense related to unvested stock options	$ 7,700,000
Total unrecognized compensation expense related to unvested stock options, expected to be recognized over a weighted average period	2 years 10 months 24 days
2012 Long-Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Plan with maximum term from the date of grant	10 years