Our corporate bonds and money market funds are classified as available-for-sale securities and carried at estimated fair value. Unrealized holding gains and losses are included in accumulated other comprehensive income (loss) in the statement of shareholders' equity. Corporate bonds with remaining maturities less than year are classified as short-term, and those with remaining maturities greater than year are classified as long-term. We consider all highly-liquid investments with maturities of months or less when purchased, including money market funds, to be cash equivalents. Gains and losses on marketable security transactions are reported on the specific-identification method.

     Contractual maturities of available-for-sale securities as of are as follows:
 

 
     Total available-for-sale securities represented approximately of our total assets. Marketable securities as of had remaining maturities between and  months.
 
     Generally accepted accounting principles establish a framework for measuring fair value, provide a definition of fair value, and prescribe required disclosures about fair-value measurements. Generally accepted accounting principles define fair value as the price that would be received to sell an asset or paid to transfer a liability. Fair value is a market-based measurement that should be determined using assumptions that market participants would use in pricing an asset or liability. Generally accepted accounting principles utilize a valuation hierarchy for disclosure of fair value measurements. The categorization within the valuation hierarchy is based on the lowest level of input that is significant to the fair value measurement. The categories within the valuation hierarchy are described as follows:
 
     Level – Financial instruments with quoted prices in active markets for identical assets or liabilities.

     Level – Financial instruments with quoted prices in active markets for similar assets or liabilities. Level  fair value measurements are determined using either prices for similar instruments or inputs that are either directly or indirectly observable, such as interest rates.

     Level – Inputs to the fair value measurement are unobservable inputs or valuation techniques.

     Money market funds are included on the balance sheets in “Cash and cash equivalents.” Corporate bonds are included on the balance sheets in “Marketable securities, short term” and “Marketable securities, long term.”
 
     The following table shows the estimated fair value of assets that were accounted for at fair value on a recurring basis:
 

     Our available-for-sale securities as of and aggregated into classes of securities, were as follows: