Fair Value of Each Stock Appreciation Rights on Date of Grant Using Black-Scholes Valuation Model (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
For stock options issued by the Company:
Risk-free interest rates	1.00%	2.20%	2.50%
Expected lives (in years)	5 years	5 years 1 month 6 days	5 years 1 month 6 days
Dividend yield	0.81%	0.80%	0.72%
Expected volatility	47.20%	46.40%	47.60%
Forfeiture rate	6.40%	7.50%	13.00%