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Stock-Based Compensation (Tables) | 6 Months Ended
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Jun. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract] |
Schedule of weighted average assumptions | The weighted average assumptions used in the Black-Scholes model for option grants to employees and directors are presented below:
| Three Months Ended June 30, |  | Six Months Ended June 30,
| 2018 |  | 2017 |  | 2018 |  | 2017
Risk-free interest rate | 2.81% |  | 1.97% |  | 2.73% |  | 2.22%
Expected volatility | 71% |  | 73% |  | 72% |  | 73%
Expected life in years | 6.1 |  | 6.0 |  | 6.2 |  | 6.0
Dividend yield | — |  | — |  | — |  | —

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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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