| 
           Investments (Details) (USD $) 
        In Thousands  | 
        1 Months Ended | 3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|---|
| 
           Jan. 31, 2010 
         | 
        
           Jun. 30, 2011 
         | 
        
           Jun. 30, 2011 
         | 
        
           Jun. 30, 2010 
         | 
        
           Dec. 31, 2010 
         | 
      |
| Investments (Textuals) [Abstract] | |||||
| Auction Rate Securities call value | $ 9,456 | ||||
| Gain on sale of auction rate securities | 425 | ||||
| Long-term restricted investments | 3,146 | 3,146 | 3,396 | ||
| Obligations under letters of credit liquidated | $ 250 | $ 250 | |||
| X | ||||||||||
| 
             
- Definition 
          Gain on sale of auction rate securities. 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          Investments Textuals Abstract. 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          The total amount of proceeds received for the sale of securities, categorized neither as held-to-maturity nor trading securities, during the reporting period. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          The cash inflow associated with the sale of investments that are pledged or subject to withdrawal restrictions during the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          This element represents the noncurrent portion of investments which are not defined as or included in marketable (debt, equity, or other) securities that are pledged or subject to withdrawal restrictions. 
  |