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Note 13 - Stock-based Compensation - Performance Stock (Details) - Performance Shares [Member] - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restricted stock (in shares)	25,707
Restricted stock, weighted-average grant date fair value (in dollars per share)	$ 58.35
Granted (in shares)	20,006	25,707
Granted, weighted-average grant date fair value (in dollars per share)	$ 105.75	$ 58.35
Restrictions lapsed (in shares)
Restrictions lapsed, weighted-average grant date fair value (in dollars per share)
Forfeited (in shares)
Forfeited, weighted-average grant date fair value (in dollars per share)
Granted (in shares)	20,006	25,707
Granted, weighted-average grant date fair value (in dollars per share)	$ 105.75	$ 58.35
Restrictions lapsed (in shares)
Restrictions lapsed, weighted-average grant date fair value (in dollars per share)
Forfeited (in shares)
Forfeited, weighted-average grant date fair value (in dollars per share)
Performance assumption change (in shares)	6,427
Performance assumption change, weighted-average grant date fair value (in dollars per share)	$ 58.35
Restricted stock (in shares)	52,140	25,707
Restricted stock, weighted-average grant date fair value (in dollars per share)	$ 76.54	$ 58.35

X

- Definition

Represents the amount of shares related to a performance change related to equity instruments other than option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

No definition available.

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- Definition

Represents the weighted average grant date fair value per share in connection to a performance change related to equity instruments other than options.

+ References

No definition available.

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- Definition

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

+ 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
-Subparagraph (c)(1)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

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
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-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(3)
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- Definition

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).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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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).

+ References

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-Publisher FASB
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-Topic 718
-SubTopic 10
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-Paragraph 2
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- Definition

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.

+ 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
-Subparagraph (c)(2)(i)-(ii)
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- Definition

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

+ References

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- Definition

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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- Definition

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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