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Fair Value Measurement (Details) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Summary of marketable securities consist of investments    
Recorded Basis $ 15,575 $ 16,878
Current Available-for-sale [Member]
   
Summary of marketable securities consist of investments    
Cost 15,580 16,874
Gross Unrealized Gains (Losses) (5) 4
Recorded Basis 15,575 16,878
Long-term Available-for-sale [Member]
   
Summary of marketable securities consist of investments    
Cost 12,954 15,428
Gross Unrealized Gains (Losses) 37 (33)
Recorded Basis 12,991 15,395
Municipal bonds [Member] | Current Available-for-sale [Member]
   
Summary of marketable securities consist of investments    
Cost 1,123 5,804
Gross Unrealized Gains (Losses) (5) 8
Recorded Basis 1,118 5,812
Fair Value Category 2  
Municipal bonds [Member] | Long-term Available-for-sale [Member]
   
Summary of marketable securities consist of investments    
Cost 296 0
Gross Unrealized Gains (Losses) 1 0
Recorded Basis 297 0
Fair Value Category 2  
Corporate bonds [Member] | Current Available-for-sale [Member]
   
Summary of marketable securities consist of investments    
Cost 14,457 11,070
Gross Unrealized Gains (Losses) 0 (4)
Recorded Basis 14,457 11,066
Fair Value Category 2  
Corporate bonds [Member] | Long-term Available-for-sale [Member]
   
Summary of marketable securities consist of investments    
Cost 10,636 14,971
Gross Unrealized Gains (Losses) 33 (33)
Recorded Basis 10,669 14,938
Fair Value Category 2  
Corporate bonds [Member] | Held-to-maturity [Member]
   
Summary of marketable securities consist of investments    
Cost 465 457
Gross Unrealized Gains (Losses) 0 0
Recorded Basis 465 457
Fair Value Category 2  
U.S. treasuries [Member] | Long-term Available-for-sale [Member]
   
Summary of marketable securities consist of investments    
Cost 1,557 0
Gross Unrealized Gains (Losses) 3 0
Recorded Basis $ 1,560 $ 0
Fair Value Category 1