Share-Based Compensation (Detail) $ / shares in Units, $ in Thousands, shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) plan shares	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) plan $ / shares shares	Jun. 30, 2014 USD ($) $ / shares
Share-based compensation
Number of share-based compensation plans | plan	1		1
Shares available for future grants | shares	2.4		2.4
Compensation cost recognized for share-based awards	$ 5,000	$ 5,200	$ 11,200	$ 10,600
Total income tax benefit recognized for share-based compensation arrangements	$ 2,100	$ 2,200	4,700	4,500
Cash received from the exercise of stock options			28,996	16,387
Actual tax benefit realized for the tax deductions from stock option exercises			$ 6,100	$ 2,200
Stock options
Share-based compensation, fair value
Weighted-average volatility (as a percent)	26.48%	27.15%	26.66%	27.35%
Dividend yield (as a percent)	1.53%	1.78%	1.55%	1.79%
Expected term	5 years 5 months 12 days	5 years 5 months 16 days	6 years 18 days	6 years 22 days
Risk-free interest rate (as a percent)	1.79%	1.92%	1.78%	1.99%
Weighted-average grant-date fair values of options granted (in dollars per share) | $ / shares			$ 21.80	$ 17.93
Total intrinsic value of options exercised			$ 14,800	$ 5,200