The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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Number of options outstanding, including both vested and non-vested options.

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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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No definition available.

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The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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The number of shares reserved for issuance pertaining to the outstanding exercisable stock options as of the balance sheet date in the customized range of exercise prices for which the market and performance vesting condition has been satisfied.

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The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices.

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The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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Weighted average exercise price as of the balance sheet date for those equity-based payment arrangements exercisable and outstanding.

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The weighted average price as of the balance sheet date at which grantees could acquire the underlying shares with respect to all outstanding stock options which are in the customized range of exercise prices.

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Weighted average remaining contractual term of outstanding stock options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Stock Options (Schedule of Qualified Stock Options Outstanding and Exercisable) (Details) - Qualified Stock Options - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding (in shares)	100,920	119,720	140,170	172,875
Options exercisable (in shares)	67,700	85,070	96,320
$26.45 - $42.70
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise price, lower range limit (in dollars per share)	$ 26.45
Range of exercise price, upper range limit (in dollars per share)	$ 42.70
Options outstanding, exercise price range (in shares)	20,870
Options outstanding, remaining contractual life	1 year 4 months 17 days
Options outstanding, exercise price (in dollars per share)	$ 34.07
Options exercisable, exercise price range (in shares)	20,870
Options exercisable, exercise price (in dollars per share)	$ 34.07
$49.44 - $74.16
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise price, lower range limit (in dollars per share)	49.44
Range of exercise price, upper range limit (in dollars per share)	$ 74.16
Options outstanding, exercise price range (in shares)	40,500
Options outstanding, remaining contractual life	3 years 7 months 20 days
Options outstanding, exercise price (in dollars per share)	$ 53.47
Options exercisable, exercise price range (in shares)	37,700
Options exercisable, exercise price (in dollars per share)	$ 53.36
$83.99 - $125.99
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise price, lower range limit (in dollars per share)	83.99
Range of exercise price, upper range limit (in dollars per share)	$ 125.99
Options outstanding, exercise price range (in shares)	39,550
Options outstanding, remaining contractual life	8 years 10 days
Options outstanding, exercise price (in dollars per share)	$ 102.28
Options exercisable, exercise price range (in shares)	9,130
Options exercisable, exercise price (in dollars per share)	$ 91.84