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Summary of Significant Accounting Policies (Tables) | 12 Months Ended
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Dec. 31, 2017
Summary of Significant Accounting Policies |
Schedule of fair value of stock options estimated at the date of grant using the Black-Scholes option-pricing model with the following weighted-average assumptions |
|  | 2017 |  |  | 2016 |  |  | 2015 |  |
Risk free interest rate |  | 1.7 | % |  | 1.3 | % |  | 1.4 | % |
Expected life |  | 4.6 | years |  | 4.6 | years |  | 4.6 | years |
Expected volatility |  | 13.0 | % |  | 15.0 | % |  | 17.0 | % |
Expected dividend yield |  | 1.0 | % |  | 1.0 | % |  | 1.0 | % |

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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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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