Annual report pursuant to Section 13 and 15(d)

Share Based Compensation - Weighted Average Assumptions Used in Calculation of Fair Value for Service Condition Awards (Detail)

v2.4.0.8
Share Based Compensation - Weighted Average Assumptions Used in Calculation of Fair Value for Service Condition Awards (Detail)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Market and performance condition awards [Member]
     
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]      
Expected volatility   44.00%  
Dividends yield   1.40%  
Expected term   5 years 2 months 12 days  
Risk-free interest rate   1.20%  
SARs [Member]
     
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]      
Expected volatility 48.40% 46.60% 48.30%
Dividends yield 2.70% 1.50% 1.80%
Expected term 5 years 3 months 18 days 6 years 2 months 12 days 6 years 4 months 24 days
Risk-free interest rate 0.70% 1.90% 2.40%
Incentive Plan and Independent Directors Stock Units [Member]
     
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]      
Expected volatility 52.10% 49.40% 48.20%
Dividends yield 2.70% 1.50% 1.70%
Expected term 3 years 9 months 18 days 3 years 9 months 18 days 3 years 9 months 18 days
Risk-free interest rate 0.40% 1.00% 1.30%