Fair Value of Each Award Estimated on Date of Grant Using Black-Scholes-Merton Option-Pricing Formula (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock Options
Schedule of Benefit Obligations Weighted Average Assumptions [Line Items]
Expected volatility, min	67.30%	61.70%	59.50%
Expected volatility, max	72.90%	71.90%	67.60%
Dividend yield, min	2.25%	1.25%	0.90%
Dividend yield, max	4.98%	2.25%	1.20%
Risk-free interest rate, min	0.36%	0.39%	0.68%
Risk-free interest rate, max	0.51%	2.18%	2.30%
Stock Options | Minimum
Schedule of Benefit Obligations Weighted Average Assumptions [Line Items]
Expected life	3 years 6 months	3 years 6 months	3 years 6 months
Stock Options | Maximum
Schedule of Benefit Obligations Weighted Average Assumptions [Line Items]
Expected life	4 years 7 months 6 days	4 years 7 months 6 days	4 years 7 months 6 days
Performance Based Restricted Stock Units (PBRSUs)
Schedule of Benefit Obligations Weighted Average Assumptions [Line Items]
Expected volatility, min	29.30%
Expected volatility, max	78.00%
Dividend yield, min	0.00%
Dividend yield, max	5.30%
Risk-free interest rate, min	0.02%
Risk-free interest rate, max	0.43%