Annual report pursuant to Section 13 and 15(d)

Employee Benefit Plans - Additional Information (Detail)

v2.4.0.6
Employee Benefit Plans - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]      
Partial withdrawal liability $ 32.6 $ 32.6  
Multiemployer defined contribution plan contributions 87.0 46.7 35.8
Four Zero One K Plan [Member]
     
Defined Benefit Plan Disclosure [Line Items]      
Percentage of contribution by employer of each employee's contribution up to 3% 100.00%    
Percentage of contribution by employer of each employee who contributes between three and six percent 50.00%    
Percentage of employee contribution, lower range 3.00%    
Percentage of employee contribution, high range 6.00%    
Contributions to all non union defined contribution plans $ 11.0 $ 9.5 $ 8.9
Red Zone [Member]
     
Defined Benefit Plan Disclosure [Line Items]      
Percentage Funded in this Zone Less than 65%    
Yellow Zone [Member]
     
Defined Benefit Plan Disclosure [Line Items]      
Percentage Funded in this Zone Less than 80%    
Green Zone [Member]
     
Defined Benefit Plan Disclosure [Line Items]      
Percentage Funded in this Zone at least 80%