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Commitments and Contingencies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Dec. 31, 2011
Commitments and Contingencies Disclosure [Line Items]          
Total rent expense $ 0.2 $ 0.6 $ 0.3 $ 1.3  
Aggregate environmental-related accruals 1.6   1.6   1.5
Threshold of ownership percentage in Company for private investigation of compliance     5.00%    
Income from contract termination     0.8    
Surety bonds | Certain development projects
         
Commitments and Contingencies Disclosure [Line Items]          
Commitment obligations 14.2   14.2   15.7
Surety bonds | Standby letters of credit
         
Commitments and Contingencies Disclosure [Line Items]          
Commitment obligations $ 0.9   $ 0.9   $ 0.8