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Stock-Based Compensation Plans (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions |  | 12 Months Ended
--- | --- | ---
Mar. 26, 2012 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Shares available for issuance |  | 125,731 |  |
Fair value of shares vested |  | $ 5.6 | $ 4.4 | $ 2.6
Intrinsic value of restricted stock units exercised |  | $ 6.9 | $ 78.7 | $ 0.2
Weighted average recognition period |  | 21 months |  |
Restricted Stock [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Weighted average fair value of shares granted |  | $ 200.79 | $ 196.96 | $ 183.30
Restricted Stock Units (RSUs) [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Weighted average fair value of shares granted |  | $ 206.45 | $ 181.04 | $ 139.00
Restricted stock units converted to common stock, shares |  | 34,836 |  |
Ten Year Vesting [Member] | Restricted Stock Units (RSUs) [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Vesting period |  | 10 years |  |
Five Year Vesting [Member] | Restricted Stock Units (RSUs) [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Vesting period |  | 5 years |  |
Three Year Vesting [Member] | Restricted Stock Units (RSUs) [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Vesting period |  | 4 years |  |
Minimum [Member] | Fifteen Year Vesting [Member] | Restricted Stock [Member] | Chief Executive Officer [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Vesting period |  | 15 years |  |
Minimum [Member] | Three Year Vesting [Member] | Restricted Stock [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Vesting period |  | 3 years |  |
Incentive Plan [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Number of additional shares authorized for issuance | 500,000 |  |  |
Total authorized shares for plan issuance |  | 2,000,000 |  |

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- Definition The number of shares converted in a noncash (or part noncash) transaction. Noncash is defined as transactions during a period that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4313-108586 + Details
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- 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=96867065&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target 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)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash. + 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 (d)(2) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + 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 (a)(3) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + 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=96867065&loc=d3e5070-113901 + Details
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