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Stock Option and Incentive Plan Schedule of Stock Options Outstanding (Details) - $ / shares | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |  |  |
Number Outstanding at period end | 540,441 | 547,129 | 547,129 | 553,312
Outstanding, Weighted Average Exercise Price | $ 96.35 | $ 96.38 | $ 96.38 | $ 97.21
Number Exercisable |  | 514,360 | 465,371 |
Exercisable, Weighted Average Exercise Price |  | $ 96.32 | $ 96.10 |
Exercise Price of $86.86 [Member] |  |  |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |  |  |
Weighted Average Remaining Contractual Life (Years) | 3 years 1 month 6 days |  |  |
Number Outstanding at period end | 118,502 |  |  |
Outstanding, Weighted Average Exercise Price | $ 86.86 |  |  |
Number Exercisable | 118,502 |  |  |
Exercisable, Weighted Average Exercise Price | $ 86.86 |  |  |
Exercise Price of $95.69 [Member] |  |  |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |  |  |
Weighted Average Remaining Contractual Life (Years) | 5 years 3 months 18 days |  |  |
Number Outstanding at period end | 54,282 |  |  |
Outstanding, Weighted Average Exercise Price | $ 95.69 |  |  |
Number Exercisable | 54,282 |  |  |
Exercisable, Weighted Average Exercise Price | $ 95.69 |  |  |
Exercise Price of $98.46 [Member] |  |  |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |  |  |
Weighted Average Remaining Contractual Life (Years) | 5 years 1 month 6 days |  |  |
Number Outstanding at period end | 202,030 |  |  |
Outstanding, Weighted Average Exercise Price | $ 98.46 |  |  |
Number Exercisable | 202,030 |  |  |
Exercisable, Weighted Average Exercise Price | $ 98.46 |  |  |
Exercise Price of $100.77 [Member] |  |  |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |  |  |
Weighted Average Remaining Contractual Life (Years) | 4 years 1 month 6 days |  |  |
Number Outstanding at period end | 165,627 |  |  |
Outstanding, Weighted Average Exercise Price | $ 100.77 |  |  |
Number Exercisable | 165,627 |  |  |
Exercisable, Weighted Average Exercise Price | $ 100.77 |  |  |
Unvested 2015 - 2017 MYLTIP Units [Member] |  |  |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |  |  |
Weighted-average period (years) | 2 years 3 months 18 days |  |  |

X
- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, 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 (i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan. + 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)(iii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan. + 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)(iii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Number of options outstanding, including both vested and non-vested options. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&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)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan. + 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=6415400&loc=d3e5070-113901 + Details
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- Definition Weighted average remaining contractual term for option awards outstanding, 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 (e)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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