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Share and Unit-based Plans - SARs Narrative (Details) - $ / shares | 12 Months Ended |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Jan. 06, 2016 | Dec. 31, 2015 | Dec. 08, 2015 | Dec. 07, 2015 | Dec. 31, 2014
SARs |  |  |  |  |  |  |
Share and unit-based plans |  |  |  |  |  |  |
Term of award (in years) | 10 years |  |  |  |  |  |
Grant date of award (in dollars per share) | $ 9.67 |  |  |  |  |  |
Volatility rate (as a percent) | 25.85% |  |  |  |  |  |
Dividend yield (as a percent) | 3.69% |  |  |  |  |  |
Risk free rate (as a percent) | 1.20% |  |  |  |  |  |
Current value (in dollars per share) | $ 59.57 |  |  |  |  |  |
Expected term (in years) | 8 years |  |  |  |  |  |
Stock appreciation units balance (shares) | 235,439 | 284,146 | 427,968 | 417,783 | 417,783 | 407,823 | 772,639
Stock appreciation weighted average price (in dollars per share) | $ 53.83 | $ 53.85 | $ 53.85 | $ 55.13 | $ 55.13 | $ 56.49 | $ 56.67
SARS granted prior to 2012 |  |  |  |  |  |  |
Share and unit-based plans |  |  |  |  |  |  |
Grant date of award (in dollars per share) | $ 7.68 |  |  |  |  |  |
Volatility rate (as a percent) | 22.52% |  |  |  |  |  |
Dividend yield (as a percent) | 5.23% |  |  |  |  |  |
Risk free rate (as a percent) | 3.15% |  |  |  |  |  |
Current value (in dollars per share) | $ 61.17 |  |  |  |  |  |
Expected term (in years) | 8 years |  |  |  |  |  |

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- Definition Represents the current value assumption that is used in valuing an equity based award. + References No definition available. + Details
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- Definition The weighted average grant date fair value at which grantees can acquire the shares reserved for issuance under the stock award plan other than options. + References No definition available. + Details
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- Definition The period of time, from the grant date until the time at which the share-based award expires. + References No definition available. + Details
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- Definition The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units. + 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 (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. + 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)(iii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The estimated measure of the 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 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)(ii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + 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://www.xbrl.org/2003/role/presentationRef -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=96867065&loc=d3e5070-113901 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Number of equity instruments other than options outstanding, including both vested and non-vested instruments. + 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 (c)(1)(i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(ii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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)(i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.D.2) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 + Details
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