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Fair Value of Financial Instruments and Concentration of Credit Risk | 12 Months Ended
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Dec. 31, 2014
Fair Value Disclosures [Abstract] |
Fair Value of Financial Instruments and Concentration of Credit Risk |
3. | Fair Value of Financial Instruments and Concentration of Credit Risk
All of our financial instruments are recognized in our consolidated balance sheet. Carrying values approximate fair value of most financial assets and liabilities. The fair value of restricted marketable securities consisting primarily of certificates of deposits, money market funds, municipal bonds, U.S. treasury bills and corporate bonds is recorded at amortized cost, which approximates fair 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 limit 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, 2014, we had significant concentrations of credit risk as follows:
| • |  | Marketable securities—$137.6 million, at fair value, in certificates of deposit.
| • |  | Marketable securities—$50.1 million, at fair value, in money market funds.
| • |  | Marketable securities—$21.7 million, at fair value, in VRDN.
| • |  | Marketable securities—$8.2 million, at fair value, in municipal bonds.
| • |  | Marketable securities—$5.7 million, at fair value, in corporate bonds.

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- Definition Tabular disclosure of all significant concentrations of risk, including credit risk and market risk, arising from all financial instruments (as defined), whether from an individual counterparty or groups of counterparties. The disclosure concerning concentrations of risk may consist of the following information: (1) for concentrations of credit risk disclosure may include: (a) information about the (shared) activity, region, or economic characteristic that identifies the concentration, (b) the maximum amount of loss due to credit risk that, based on the gross fair value of the financial instrument, the entity would incur if parties to the financial instruments that make up the concentration failed completely to perform according to the terms of the contracts and the collateral or other security, if any, for the amount due proved to be of no value to the entity, (c) the policy of requiring collateral or other security to support financial instruments subject to credit risk, information about the entity's access to that collateral or other security, and the nature and a brief description of the collateral or other security supporting those financial instruments, and (d) the policy of entering into master netting arrangements to mitigate the credit risk of financial instruments, information about the arrangements for which the entity is a party, and a brief description of the terms of those arrangements, including the extent to which they would reduce the entity's maximum amount of loss due to credit risk and (2) for disclosure of quantitative information about the market risks of financial instruments that is consistent with the way the company manages or adjusts those risks, disclosure may include: (a) more details about current positions and perhaps activity during the period, (b) the hypothetical effects on comprehensive income (or net assets), or annual income, of several possible changes in market prices, (c) a gap analysis of interest rate re-pricing or maturity dates, (d) the duration of the financial instruments, (e) the entity's value at risk from derivatives and from other positions at the end of the reporting period and the average value at risk during the year, or (f) other ways of reporting quantitative information as internally developed. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13531-108611 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 21 -URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13537-108611 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 23 -URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13587-108611 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 22 -URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13572-108611 + Details
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