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Share-Based Transactions - Nonemployee Share-Based Transactions, Valuation Assumptions (Details) - Nonemployee Shares [Member] - $ / shares | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Valuation Assumptions For Restricted Stock Units [Line Items] |  |
Expected volatility, Minimum | 18.00% | 24.00%
Expected volatility, Maximum | 34.00% | 42.00%
Minimum [Member] |  |
Valuation Assumptions For Restricted Stock Units [Line Items] |  |
Quarterly dividends expected | $ 0.19 | $ 0.17
Maximum [Member] |  |
Valuation Assumptions For Restricted Stock Units [Line Items] |  |
Quarterly dividends expected | $ 0.20 | $ 0.18
Risk-free interest rates | 3.00% | 2.00%

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- Definition Share based compensation arrangement by share based payment award fair value assumptions expected dividend rate range. + References No definition available. + Details
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- Definition Valuation assumptions for restricted stock units. + References No definition available. + Details
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- Definition The estimated measure of the maximum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + References No definition available. + Details
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- Definition The estimated measure of the minimum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + References No definition available. + Details
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- Definition The risk-free interest rate assumption that is used in valuing an option on its own shares. + 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)(iv) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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