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Fair Value Of Financial Instruments And Concentration Of Credit Risk
12 Months Ended
Dec. 31, 2011
Fair Value Of Financial Instruments And Concentration Of Credit Risk [Abstract]  
Fair Value Of Financial Instruments And Concentration Of Credit Risk
2. Fair Value of Financial Instruments and Concentration of Credit Risk

All of our financial instruments are recognized in our balance sheet. Carrying values approximate fair value of most financial assets and liabilities. The fair value of restricted marketable securities consisting primarily of U.S. Treasury bills and municipal bonds was recorded at amortized cost which approximates market value for similar instruments. The interest rates on our restricted marketable security investments approximate current market rates for these types of investments; therefore, the recorded value of the restricted marketable securities approximates fair value.

Financial instruments that potentially subject us to concentration of credit risk consist primarily of temporary cash investments, marketable securities, restricted marketable securities and trade accounts receivable. We restrict investment of temporary cash investments and marketable securities to financial institutions with high credit ratings, corporate bonds and to investments in governmental debt instruments. Credit risk on trade receivables is minimized as a result of the large and diverse nature of our customer base.

At December 31, 2011, we had significant concentrations of credit risk as follows:

 

  - Cash and cash equivalents—approximately $44.5 million of the Company's cash and cash equivalents at December 31, 2011 were invested in tax-exempt money market funds. Fair value was determined using quoted prices in active markets for identital securities.

 

  - Marketable securities—All investments are held in publicly-traded securities, which includes $11.4 million, at fair value, in municipal bonds.