Note 8 - Share-based Compensation - Stock Option Activity (Details)	9 Months Ended
Sep. 30, 2018 USD ($) $ / shares shares
Balance, shares (in shares) \| shares	24,000
Balance, weighted average exercise price (in dollars per share) \| $ / shares	$ 24.15
Options granted, shares (in shares) \| shares
Options granted, weighted average exercise price (in dollars per share) \| $ / shares
Options exercised, shares (in shares) \| shares
Options exercised, weighted average exercise price (in dollars per share) \| $ / shares
Options canceled, shares (in shares) \| shares
Options canceled, weighted average exercise price (in dollars per share) \| $ / shares
Balance, shares (in shares) \| shares	24,000
Balance, weighted average exercise price (in dollars per share) \| $ / shares	$ 24.15
Balance, weighted average remaining contractual life (Year)
Balance, aggregate instrinsic value \| $
Exercisable, shares (in shares) \| shares	24,000
Exercisable, weighted average exercise price (in dollars per share) \| $ / shares	$ 24.15
Exercisable, weighted average remaining contractual life (Year)	1 year 182 days
Exercisable, aggregate instrinsic value \| $

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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- Definition

The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

+ References

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- Definition

For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

+ References

+ Details

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- Definition

Weighted average price of options that were either forfeited or expired.

+ References

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- Definition

Gross number of share options (or share units) granted during the period.

+ References

No definition available.

+ Details

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- Definition

Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

+ References

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- Definition

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

+ 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
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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-Publisher FASB
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-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

+ References

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- Definition

Weighted average price at which option holders acquired shares when converting their stock options into shares.

+ References

No definition available.

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- Definition

Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

+ References

No definition available.

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- Definition

Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

+ References

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- Definition

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

+ References

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- Definition

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

+ References

+ Details

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- Definition

Number of share options (or share units) exercised during the current 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
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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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Note 8 - Share-based Compensation - Stock Option Activity (Details)	9 Months Ended
	Sep. 30, 2018 USD ($) $ / shares shares
Balance, shares (in shares) \| shares	24,000
Balance, weighted average exercise price (in dollars per share) \| $ / shares	$ 24.15
Options granted, shares (in shares) \| shares
Options granted, weighted average exercise price (in dollars per share) \| $ / shares
Options exercised, shares (in shares) \| shares
Options exercised, weighted average exercise price (in dollars per share) \| $ / shares
Options canceled, shares (in shares) \| shares
Options canceled, weighted average exercise price (in dollars per share) \| $ / shares
Balance, shares (in shares) \| shares	24,000
Balance, weighted average exercise price (in dollars per share) \| $ / shares	$ 24.15
Balance, weighted average remaining contractual life (Year)
Balance, aggregate instrinsic value \| $
Exercisable, shares (in shares) \| shares	24,000
Exercisable, weighted average exercise price (in dollars per share) \| $ / shares	$ 24.15
Exercisable, weighted average remaining contractual life (Year)	1 year 182 days
Exercisable, aggregate instrinsic value \| $