Stock-Based Compensation Plans - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 Year	Sep. 30, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued under the ESPP			30,021	45,642
Incentive plan, weighted-average grant date fair value of stock options granted			$ 13.69	$ 9.39
Incentive plan, total intrinsic value of stock options exercised			$ 4,500,000	$ 1,200,000
Proceeds from exercises of stock options			2,780,000	2,508,000
Actual tax benefit realized for the tax deductions from option exercises			1,600,000	400,000
Incentive plan, percentage of options expected to vest over the vesting period	94.90%		94.90%
Dividend yield			0.00%
Unrecognized compensation costs	4,500,000		4,500,000
Unrecognized compensation costs weighted-average recognition periods			1.6
Stock-based compensation expenses	2,200,000	1,900,000	6,691,000	5,455,000
Stock-based compensation expenses tax benefits	700,000	700,000	2,400,000	2,000,000
Employee Stock Purchase Plan 1999
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance	1,500,000		1,500,000
Permitted designation for the purchase of common stock under the ESPP			Participating employees are permitted to designate up to the lesser of $25,000 or 10% of their annual base compensation for the purchase of common stock under the ESPP. Purchases under the ESPP are made one calendar month after the end of each fiscal quarter.
Employee participating annual base compensation designated for purchase of common stock, amount	25,000		25,000
Employee participating annual base compensation designated for purchase of common stock, Percent	10.00%		10.00%
Price of common stock purchased under the ESPP			The price for shares of common stock purchased under the ESPP is 85% of the stock’s fair market value on the last business day of the three-month participation period.
Price of common stock purchased under the ESPP, Percent			85.00%
Restricted share awards (RSAs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested Number of Shares, Vested			79,550
Incentive plan, shares withheld to pay employees' portion of the minimum payroll withholding taxes			23,370
Unrecognized compensation costs	1,300,000		1,300,000
Unrecognized compensation costs weighted-average recognition periods			1.3
LTIP Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs	$ 5,100,000		$ 5,100,000
Unrecognized compensation costs weighted-average recognition periods			1.9