Stock Plans (Schedule of Non-Vested Restricted Stock Units Activity) (Details) - Restricted Stock [Member] - $ / shares	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested balance at January 1,	29,960	20,704	21,962
Granted	12,901	19,250	13,224
Forfeited	(126)
Vested	(15,574)	(9,994)	(14,482)
Non-vested balance at December 31,	27,161	29,960	20,704
Weighted-average grant date fair value, Non-vested balance at January 1,	$ 38.99	$ 23.59	$ 20.31
Weighted-average grant date fair value, Granted	54.70	47.44	25.36
Weighted-average grant date fair value, Forfeited	54.69
Weighted-average grant date fair value, Vested	33.81	23.69	20.47
Weighted-average grant date fair value, Non-vested balance at December 31,	$ 49.48	$ 38.99	$ 23.59
Director Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested balance at January 1,	12,600	8,400	8,400
Granted	5,600	8,400	8,400
Forfeited
Vested	(7,000)	(4,200)	(8,400)
Non-vested balance at December 31,	11,200	12,600	8,400
Weighted-average grant date fair value, Granted	$ 54.69	$ 49.50	$ 26.17
Omnibus Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested balance at January 1,	17,360	12,304	13,562
Granted	7,301	10,850	4,824
Forfeited	(126)
Vested	(8,574)	(5,794)	(6,082)
Non-vested balance at December 31,	15,961	17,360	12,304

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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)(1)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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The number of grants made 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).

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-Publisher FASB
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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).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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-Publisher FASB
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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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-Publisher FASB
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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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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.

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