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Marketable Securities Marketable Securities (Tables) | 6 Months Ended
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Jun. 30, 2019
Marketable Securities [Abstract] |
Available-for-sale Securities [Table Text Block] | The schedule of maturities at June 30, 2019 and December 31, 2018 is as follows:
| Maturities as of June 30, 2019 |  | Maturities as of December 31, 2018
| 1 Year or Less |  | 1 to 4 Years |  | 1 Year or Less |  | 1 to 4 Years
Corporate bonds | $ | 2,150 |  |  | $ | — |  |  | $ | 24,617 |  |  | $ | — |
Certificates of deposit | 33,946 |  |  | — |  |  | 42,351 |  |  | — |
Total | $ | 36,096 |  |  | $ | — |  |  | $ | 66,968 |  |  | $ | — |

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- Definition Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities. + References No definition available. + Details
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- References No definition available. + Details
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