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Commitments and Contingencies (Details 2) (USD $)
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Commitments and Contingencies      
Deductible per claim for each line of coverage, until claim aggregate is reached $ 1,000,000    
Deductible per claim, once a policy's claim aggregate is reached per line of coverage 500,000    
Deductible under health insurance benefits for qualified individuals 100,000    
Roll forward of activity in the insurance reserves      
Balance at beginning of period 38,850,000 34,044,000  
Net increases in reserves 19,473,000 23,621,000  
Net payments made (19,010,000) (18,815,000)  
Balance at end of period 39,583,000 38,850,000  
Number of multi-employer pension plans, the withdrawal of which could result in assessment of liabilities for additional contributions related to the underfunding of plans, minimum 1    
Potential number of litigation claims in which an adverse outcome could result, minimum 1    
Insurance and Claims Accruals
      
Roll forward of activity in the insurance reserves      
Insurance expense 20,900,000 21,500,000 16,000,000
Surety bonds
      
Commitments and Contingencies      
Aggregate original face amount of outstanding bonds issued by the surety 883,300,000    
Estimated remaining cost to complete bonded projects $ 301,400,000