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Concentration of Credit Risk | 12 Months Ended
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Dec. 31, 2017
Risks And Uncertainties [Abstract] |
Concentration of Credit Risk | Note 2 - Concentration of Credit Risk Financial instruments that potentially subject us to concentration of credit risk consist primarily of cash equivalents, investments, restricted cash and investments, and trade accounts receivable. We limit investment of cash equivalents and investments to financial institutions with high credit ratings. Credit risk on trade accounts is minimized as a result of the large and diverse nature of our customer base. At December 31, 2017, we had concentrations of credit risk as follows:
| • | $184.7 million, at fair value, in corporate bonds.
| • | $86.2 million, at fair value, in mortgage backed securities.
| • | $46.2 million, at fair value, in U.S. treasuries.
| • | $38.0 million, at fair value, in U.S. government agency securities.
| • | $19.0 million, at fair value, in commercial paper.
| • | $16.1 million, at fair value, in money market funds.

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- Definition The entire disclosure for any concentrations existing at the date of the financial statements that make an entity vulnerable to a reasonably possible, near-term, severe impact. This disclosure informs financial statement users about the general nature of the risk associated with the concentration, and may indicate the percentage of concentration risk as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -URI http://asc.fasb.org/topic&trid=2134479 + Details
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- References No definition available. + Details
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