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Fair Value Measurement (Details 1) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Summary of company's restricted marketable securities and workers' compensation deposits    
Cost $ 8,735 $ 7,295
Gross Unrealized Gains 22 16
Recorded Basis 16,748 16,878
Municipal bonds [Member]
   
Summary of company's restricted marketable securities and workers' compensation deposits    
Cost 4,920 5,580
Gross Unrealized Gains 17 17
Recorded Basis 4,937 5,597
Fair Value Category 2  
Corporate bonds [Member]
   
Summary of company's restricted marketable securities and workers' compensation deposits    
Cost 2,035 148
Gross Unrealized Gains 5 (1)
Recorded Basis 2,040 147
Fair Value Category 2  
U.S. Treasuries [Member]
   
Summary of company's restricted marketable securities and workers' compensation deposits    
Cost 1,780 1,567
Gross Unrealized Gains 0 0
Recorded Basis 1,780 1,567
Fair Value Category $ 1