Note 5 - Share-based Compensation - Summary of Status of Company's Stock Options (Details)	3 Months Ended
Mar. 31, 2017 USD ($) $ / shares shares
Balance (in shares) \| shares	26,000
Balance (in dollars per share) \| $ / shares	$ 24.97
Options granted (in shares) \| shares
Options granted (in dollars per share) \| $ / shares
Options exercised (in shares) \| shares
Options exercised (in dollars per share) \| $ / shares
Options canceled (in shares) \| shares
Options canceled (in dollars per share) \| $ / shares
Balance (in shares) \| shares	26,000
Balance (in dollars per share) \| $ / shares	$ 24.97
Balance (Year)
Balance \| $
Exercisable, March 31, 2017 (in shares) \| shares	26,000
Exercisable, March 31, 2017 (in dollars per share) \| $ / shares	$ 24.97
Exercisable, March 31, 2017 (Year)	2 years 284 days
Exercisable, March 31, 2017 \| $

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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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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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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)-(4)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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-Subparagraph (c)(1)(iv)(3)-(4)
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Gross number of share options (or share units) granted during the period.

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No definition available.

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

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

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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

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No definition available.

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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.

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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.

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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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Number of share options (or share units) exercised during the current period.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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Note 5 - Share-based Compensation - Summary of Status of Company's Stock Options (Details)	3 Months Ended
	Mar. 31, 2017 USD ($) $ / shares shares
Balance (in shares) \| shares	26,000
Balance (in dollars per share) \| $ / shares	$ 24.97
Options granted (in shares) \| shares
Options granted (in dollars per share) \| $ / shares
Options exercised (in shares) \| shares
Options exercised (in dollars per share) \| $ / shares
Options canceled (in shares) \| shares
Options canceled (in dollars per share) \| $ / shares
Balance (in shares) \| shares	26,000
Balance (in dollars per share) \| $ / shares	$ 24.97
Balance (Year)
Balance \| $
Exercisable, March 31, 2017 (in shares) \| shares	26,000
Exercisable, March 31, 2017 (in dollars per share) \| $ / shares	$ 24.97
Exercisable, March 31, 2017 (Year)	2 years 284 days
Exercisable, March 31, 2017 \| $