Stock-Based Compensation Plans - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued under ESPP	9,606	12,483
Incentive plan, percentage of options expected to vest over the vesting period	94.20%
Incentive plan, weighted-average grant date fair value of stock options granted	$ 21.73	$ 18.51
Incentive plan, total intrinsic value of stock options exercised	$ 4,300,000	$ 7,000,000
Dividend yield
Stock-based compensation expenses	3,950,000	5,618,000
Stock-based compensation expenses tax benefits	1,500,000	2,000,000
Proceeds from exercises of stock options	3,864,000	4,399,000
Actual tax benefit realized from tax deductions of option exercises	1,600,000	2,500,000
Restricted share awards (RSAs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards, shares vested	3,333
Shares withheld to pay employees	1,575
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	3,400,000
Unrecognized compensation costs, weighted-average recognition periods	2 years 6 months
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs	9,300,000
Unrecognized compensation costs, weighted-average recognition periods	2 years 3 months 18 days
LTIP Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards, shares vested	327,576
Shares withheld to pay employees	112,754
Unrecognized compensation costs	14,900,000
Unrecognized compensation costs, weighted-average recognition periods	2 years 3 months 18 days
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 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%