Note 6 - Equity-based Compensation - Stock Option Activities (Details) - $ / shares	9 Months Ended	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Outstanding (in shares)	207,108	34,190	34,190
Outstanding, weighted average exercise price (in dollars per share)	$ 14.18	$ 9.65	$ 9.65
Outstanding, average remaining contractual term (Year)	6 years	1 year 292 days	6 years 73 days	2 years 109 days
Granted (in shares)	5,000	0
Granted, weighted average exercise price (in dollars per share)	$ 15.48	$ 0
Exercised (in shares)	(15,464)	0
Exercised, weighted average exercise price (in dollars per share)	$ 9.65	$ 0
Forfeited or expired (in shares)	(7,734)	0
Forfeited or expired, weighted average exercise price (in dollars per share)	$ 11.08	$ 0
Outstanding (in shares)	188,910	34,190	207,108	34,190
Outstanding, weighted average exercise price (in dollars per share)	$ 14.71	$ 9.65	$ 14.18	$ 9.65
Exercisable (in shares)	7,260	34,190
Exercisable, weighted average exercise price (in dollars per share)	$ 9.65	$ 9.65
Exercisable, average remaining contractual term (Year)	292 days	1 year 292 days

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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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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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.

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

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

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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.

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Number of share options (or share units) exercised during the current period.

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