Share-Based Compensation - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended
	Apr. 30, 2011	Dec. 31, 2011
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Number of shares available for issuance		1,386,360
Expected volatility term		5 years
Closing stock price		47.69
Equity Incentive Plan
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Maximum aggregate number of shares that may be awarded and sold		3,000,000
Number of shares available for Grant additional shares approved in period	425,000
Options granted under the 2006 Incentive Plan, expiration period		7 years
Options, exercisable period		4 years
Equity Incentive Plan | Restricted stock units | Lower Limit
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Vesting period		3 years
Equity Incentive Plan | Performance-Based Restricted Stock | Lower Limit
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Vesting period		12 months
Employee Stock Purchase Plan
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Maximum percentage of gross compensation that participating employees may annually contribute towards ESPP		10.00%
Maximum amount that participating employees may annually contribute towards ESPP		25,000
Percentage of fair market value of common stock at which employees may purchase shares under ESPP		85.00%
Number of shares issued under ESPP		149,327
Proceeds from issuance of shares under ESPP		6,600,000
Number of shares available for issuance		1,075,421