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Commitments and Contingencies (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2013
item
Dec. 31, 2012
item
Dec. 31, 2011
Commitments and Contingencies      
Irrevocable standby letters of credit outstanding $ 18.4 $ 19.7  
Number of letters of credit related to the payment obligation under insurance programs 1 1  
Letters of credit outstanding related to the payment obligation under insurance programs 17.5 17.5  
Letters of credit outstanding related to contract performance obligations 0.9 2.2  
Leases      
Number of leases that included guaranteed residual values 0    
Future minimum lease payments for operating leases      
2014 1.9    
2015 0.9    
2016 0.4    
2017 0.2    
2018 0.2    
Thereafter 0.2    
Operating lease, additional disclosure      
Rent expense 51.2 43.1 32.2
Purchase Commitments for Construction Equipment      
Outstanding purchase orders for certain construction equipment $ 6.1    
Scheduled period of time for cash outlay 5 months    
Minimum
      
Leases      
Term of operating lease 1 year    
Maximum
      
Leases      
Term of operating lease 7 years