Note 11 - Stock Option Plans - Stock Option Transactions (Details) - $ / shares	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Outstanding, Number of shares (in shares)	513,366	976,062	1,407,639
Outstanding, Weighted average exercise price per share (in dollars per share)	$ 9.24	$ 5.41	$ 3.80
Granted, Number of shares (in shares)	81,750	67,500	102,475
Granted, Weighted average exercise price per share (in dollars per share)	$ 22.66	$ 21.26	$ 15.78
Exercised, Number of shares (in shares)	(109,963)	(517,998)	(502,061)
Exercised, Weighted average exercise price per share (in dollars per share)	$ 3.79	$ 3.53	$ 2.95
Forfeited, Number of shares (in shares)	(9,902)	(10,323)	(28,366)
Forfeited, Weighted average exercise price per share (in dollars per share)	$ 16.80	$ 13.30	$ 6.60
Expired, Number of shares (in shares)	(750)	(1,875)	(3,625)
Expired, Weighted average exercise price per share (in dollars per share)	$ 3.76	$ 2.40	$ 3.36
Outstanding, Number of shares (in shares)	474,501	513,366	976,062
Outstanding, Weighted average exercise price per share (in dollars per share)	$ 12.67	$ 9.24	$ 5.41
Options exercisable, Number of shares (in shares)	332,192	321,155	725,392
Options exercisable, Weighted average exercise price per share (in dollars per share)	$ 10.08	$ 6.49	$ 4.03

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=6415400&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.

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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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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.

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

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

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

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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 price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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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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