Stock Based Compensation (Awards of Restricted Stock) (Details) - Restricted Stock [Member]	9 Months Ended
Sep. 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

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).

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 (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

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No definition available.

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- Definition

Net number of non-option equity instruments granted to participants.

+ 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
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-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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