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Marketable Securities
6 Months Ended
Jun. 30, 2013
Marketable Securities [Abstract]  
Marketable Securities
Marketable Securities
Marketable securities consist primarily of corporate bonds and certificates of deposit with maturities greater than three months and up to ten years at the time of purchase as well as marketable equity securities. These securities, which are classified as available-for-sale, are carried at fair value, with unrealized gains and losses, net of any tax effect, reported in stockholders’ equity as accumulated other comprehensive income (loss). These securities are classified as current and non-current marketable securities based upon their maturities. Amortization of premiums and discounts is included in interest income. For the three and six months ended June 30, 2013, the amortization of bond premiums totals $173 and $360, respectively, compared to $279 and $529 for the comparable periods in 2012. The values of these securities may fluctuate as a result of changes in equity values, market interest rates and credit risk.