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Our investment policy provides limitations for issuer concentration, which limits, at the time of purchase, the concentration in any one issuer to 5% of the market value of our total investment portfolio. 

We review our investment portfolio for potential “other-than-temporary” declines in value on an individual investment basis. We assess, on a quarterly basis, significant declines in value which may be considered other-than-temporary and, if necessary, recognize and record the appropriate charge to write-down the carrying value of such investments. In making this assessment, we take into consideration qualitative and quantitative information, including but not limited to the following: the magnitude and duration of historical declines in market prices, credit rating activity, assessments of liquidity, public filings, and statements made by the issuer. We generally begin our identification of potential other-than-temporary impairments by reviewing any security with a fair value that has declined from its original or adjusted cost basis by 25% or more for six or more consecutive months. We then evaluate the individual security based on the previously identified factors to determine the amount of the write-down, if any. As a result of our review, we recorded an other-than-temporary impairment charge of $11 thousand during the fourth quarter of 2013. For each of the years ended December 31, 2013, 2012 and 2011 we recorded a charge of $25 thousand, $0.7 million and $68 thousand, respectively, related to the other-than-temporary impairment of certain marketable equity securities and our deferred compensation plan assets. 

Realized gains and losses on sales of securities are computed under the specific identification method. The following table presents gross realized gains and losses related to our investments for the years ended December 31, 2013, 2012 and 2011: 

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The following table presents the breakdown of investments with unrealized losses at December 31, 2013: 

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The following table presents the breakdown of investments with unrealized losses at December 31, 2012. 

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The decrease in unrealized losses during 2013, as reflected in the table above, is primarily due to the restructuring of our investment portfolio relating to marketable equity securities in December 2013 resulting in the sale of several securities in an unrealized loss position. At December 31, 2013, a total of 168 of our marketable equity securities were in an unrealized loss position. 

