Stock-Based Compensation Plans - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended				9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Jun. 14, 2012 2005 Stock Incentive Plan	Jun. 14, 2012 2005 Stock Incentive Plan Second Amendment	Sep. 30, 2012 Restricted share awards (RSAs)	Sep. 30, 2012 S1 2003 Stock Incentive Plan	Sep. 30, 2012 Stock Options	Sep. 30, 2012 LTIP Performance Shares	Sep. 30, 2012 Employee Stock Purchase Plan 1999
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized					5,000,000	7,750,000					1,500,000
Permitted designation for purchase of common stock under 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
Employee participating annual base compensation designated for purchase of common stock, percent											10.00%
Price of common stock purchased under ESPP, description											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 ESPP, percent											85.00%
Shares issued under ESPP			30,131	30,021
Incentive plan, percentage of options expected to vest over the vesting period	94.50%		94.50%
Incentive plan, weighted-average grant date fair value of stock options granted			$ 22.89	$ 13.69
Incentive plan, total intrinsic value of stock options exercised			16,000,000	4,500,000
Dividend yield
Restricted shares awards, shares vested							74,482	83,016
Restricted shares withheld to pay employees' portion of minimum payroll withholding taxes							22,284	32,080
Restricted share awards, vesting increments on anniversary dates of grants							25.00%
Awards granted requisite service period							4 years
Vesting percentage if employee is terminated without cause within 12 months from acquisition date							100.00%
Unrecognized compensation costs							4,300,000		5,700,000	7,800,000
Unrecognized compensation costs, weighted-average recognition periods							2 years 10 months 24 days		1 year 9 months 18 days	1 year 9 months 18 days
Stock-based compensation expenses	2,600,000	2,200,000	11,661,000	6,691,000
Stock-based compensation expenses tax benefits	900,000	700,000	4,200,000	2,400,000
Proceeds from exercises of stock options			15,059,000	2,780,000
Actual tax benefit realized from tax deductions of option exercises			$ 5,800,000	$ 1,600,000