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Stock Based Compensation (Awards of Restricted Stock) (Details) - Restricted Stock [Member] | 6 Months Ended
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Jun. 30, 2018 $ / shares shares
Ratably Over Period [Member] | 2/15/2018 | Employee Stock [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Shares Granted | shares | 39,950
Grant Date Fair Value Per Share | $ / shares | $ 71.75
Vesting Period | Ratably over 5 years from grant date
Ratably Over Period [Member] | 2/27/2018 | Employee Stock [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Shares Granted | shares | 1,150
Grant Date Fair Value Per Share | $ / shares | $ 72.60
Vesting Period | Ratably over 5 years from grant date
Ratably Over Period [Member] | 5/15/2018 | Employee Stock [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Shares Granted | shares | 530
Grant Date Fair Value Per Share | $ / shares | $ 74.00
Vesting Period | Ratably over 5 years from grant date
Immediate Vest on grant date [Member] | 5/22/2018 | Two Thousand Eighteen Nonemployee Director Stock Plan [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Shares Granted | shares | 6,000
Grant Date Fair Value Per Share | $ / shares | $ 76.58
Vesting Period | Shares vested immediately

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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 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 Net number of non-option equity instruments granted to participants. + 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)(iv)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Description of pertinent provisions of equity-based compensation awards that have actual or potential impact upon the company's financial statements. + 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) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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