Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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

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Percentage of vesting of award under share-based payment arrangement.

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Stock Plans (Summary of Weighted-Average Fair-Value and Vesting of Restricted Stock Grants) (Details) - $ / shares		12 Months Ended
	Feb. 05, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Director Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		3 years	3 years	2 years
Director Plan [Member] \| Share-based Payment Arrangement, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, percentage per year		33.00%	33.00%	50.00%
Director Plan [Member] \| Share-based Payment Arrangement, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, percentage per year		33.00%	33.00%	50.00%
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted		12,901	19,250	13,224
Weighted-average grant date fair value		$ 54.70	$ 47.44	$ 25.36
Restricted Stock [Member] \| Director Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	5,600	5,600	8,400	8,400
Weighted-average grant date fair value		$ 54.69	$ 49.50	$ 26.17
Award Date One [Member] \| Omnibus Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		3 years	3 years	3 years
Award Date One [Member] \| Omnibus Plan [Member] \| Share-based Payment Arrangement, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, percentage per year		33.00%	33.00%	33.00%
Award Date One [Member] \| Omnibus Plan [Member] \| Share-based Payment Arrangement, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, percentage per year		33.00%	33.00%	33.00%
Award Date One [Member] \| Omnibus Plan [Member] \| Share-based Payment Arrangement, Tranche Three [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, percentage per year		33.00%	33.00%	33.00%
Award Date One [Member] \| Restricted Stock [Member] \| Omnibus Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	7,251	7,251	10,800	4,749
Weighted-average grant date fair value		$ 54.69	$ 45.83	$ 23.93
Vesting period	3 years
Award Date Two [Member] \| Omnibus Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		1 year	1 year	1 year
Award Date Two [Member] \| Restricted Stock [Member] \| Omnibus Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted		50	50	75
Weighted-average grant date fair value		$ 58.08	$ 49.50	$ 26.17