Fair Values of all Options Granted Estimated Using Binomial Option-Pricing Model with Weighted-average Assumptions (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	2.17%	1.72%	0.27%
Weighted average expected volatility	50.90%	46.87%	45.06%
Weighted average risk-free interest rate	1.14%	2.58%	2.91%
Weighted average expected lives (in years)	5 years 4 months 6 days	5 years 8 months 12 days	5 years 9 months 29 days
Weighted average grant-date fair value	$ 7.85	$ 7.76	$ 6.65