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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES. (Tables) | 12 Months Ended
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Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract] |
Assumptions used in option pricing model and grant date fair value of options | We used the following inputs to the Black-Scholes option-pricing model to estimate the fair value of each option granted in 2015 and 2016.
| Weighted-average
| 2015 |  | 2016
Grant-date fair value per option awarded | $ | 17.35 |  |  | $ | 10.62 |
Assumptions used: |  |  |
Expected life in years | 7.0 |  |  | 6.8 |
Expected volatility | 27 | % |  | 20 | %
Dividend yield | 2.4 | % |  | 2.5 | %
Risk-free interest rate | 1.9 | % |  | 1.6 | %

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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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