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Properties and Equipment - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
1 Months Ended 12 Months Ended
Jul. 31, 2008
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Sale Leaseback Transaction [Line Items]        
Net proceeds received from sale-leaseback transactions $ 35.8      
Deferred gain on sale-leaseback transactions 29.0 19.4 21.4  
Lease period for sale-leaseback transactions 15 years      
Rental expense   8.9 8.8 9.1
Minimum future rental commitments   51.9    
Minimum future rental commitments, year one   7.8    
Minimum future rental commitments, year two   6.0    
Minimum future rental commitments, year three   5.4    
Minimum future rental commitments, year four   5.4    
Minimum future rental commitments, year five   4.9    
Minimum future rental commitments, thereafter   $ 22.4