Note 6 - Share-based Compensation - Restricted Stock Unit Activity (Details) - Restricted Stock Units (RSUs) [Member]	3 Months Ended
Mar. 31, 2021 $ / shares shares
Outstanding, restricted stock units (in shares) \| shares	93,187
Outstanding, weighted average award date fair value (in dollars per share) \| $ / shares	$ 35.03
Awarded, restricted stock units (in shares) \| shares	45,292
Awarded, weighted average award date fair value (in dollars per share) \| $ / shares	$ 49.14
Shares vested, restricted stock units (in shares) \| shares	(33,987)
Shares vested, weighted average award date fair value (in dollars per share) \| $ / shares	$ 31.29
Outstanding, restricted stock units (in shares) \| shares	104,492
Outstanding, weighted average award date fair value (in dollars per share) \| $ / shares	$ 42.72

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
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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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).

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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
-Name Accounting Standards Codification
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-Section 50
-Paragraph 2
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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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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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