Stock-Based Compensation Plans - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued under the ESPP	12,483	11,373
Incentive plan, percentage of options expected to vest over the vesting period	94.60%
Incentive plan, weighted-average grant date fair value of stock options granted	$ 18.51	$ 0.00
Incentive plan, total intrinsic value of stock options exercised	$ 7,000,000	$ 2,800,000
Dividend yield	0.00%
Stock-based compensation expenses	5,618,000	2,369,000
Stock-based compensation expenses tax benefits	2,000,000	900,000
Proceeds from exercises of stock options	4,399,000	1,782,000
Actual tax benefit realized for the tax deductions from option exercises	2,500,000	1,100,000
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
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. 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.
Employee participating annual base compensation designated for purchase of common stock, amount	25,000
Employee participating annual base compensation designated for purchase of common stock, percent	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%
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs	6,300,000
Unrecognized compensation costs, weighted-average recognition periods	2.1
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs	3,500,000
Unrecognized compensation costs, weighted-average recognition periods	3.0
LTIP Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs	$ 11,800,000
Unrecognized compensation costs, weighted-average recognition periods	2.1
Restricted share awards (RSAs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares awards, shares vested	37,583
Restricted shares withheld to pay employees' portion of minimum payroll withholding taxes	11,152
Restricted Share Awards, vesting increments on the anniversary dates of grants	25.00%
Awards granted requisite service period	4 years
Stock Incentive Plan 2003
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares awards, shares vested	67,857
Restricted shares withheld to pay employees' portion of minimum payroll withholding taxes	27,310