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Note 6 - Share-based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized |  | 5,000,000 |  | 5,000,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant |  | 3,456,944 |  | 3,456,944 |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term |  |  |  | 5 years |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number |  | 667,784 |  | 667,784 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares, Ending Balance |  | 43,245 |  | 43,245 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term |  |  |  | 1 year 306 days |
Share-based Compensation Arrangement by Share-based Payment Award Options Vested and Expected to Vest Exercisable Intrinsic Value |  | $ 3,200 |  | $ 3,200 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term |  |  |  | 3 years 30 days |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value |  | $ 100 | $ 400 | $ 900 | $ 2,700
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross |  | 43,245 | 53,970 | 141,630 | 155,142
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value |  | $ 4.39 | $ 6.40 | $ 5.93 | $ 5.56
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options |  | $ 200 |  | $ 200 |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition |  |  |  | 1 year 211 days |
Proceeds from Stock Options Exercised |  | 100 | $ 400 | $ 432 | $ 1,218
Shares Received from Stock Options Exercised |  |  |  | 400,000 | 1,200,000
Stock Issued During Period, Shares, New Issues |  |  |  | 26,234 | 113,143
Employee Service Share-based Compensation, Tax Benefit from Exercise of Stock Options |  | $ 100 | $ 100 | $ 100 | $ 300
Common Stock [Member] |  |  |  |  |
Shares Received from Stock Options Exercised |  | 0 | 0 | 6,894 | 43,841
Stock Issued During Period, Shares, New Issues |  |  |  | 26,234 | 113,143
Employee Stock Option [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term | [1] | 3 years | 5 years |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition |  |  |  | 1 year 306 days |
Employee Stock Option [Member] | Minimum [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term | [1] |  |  | 3 years | 5 years
Employee Stock Option [Member] | Maximum [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term | [1] |  |  | 10 years | 10 years
Stock Appreciation Rights (SARs) [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term | [1] |  |  | 3 years | 5 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term |  |  |  | 2 years 300 days |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding |  | $ 200 |  | $ 200 |
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted |  |  |  | 48,515 | 43,988
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value |  |  |  | $ 6.06 | $ 4.83
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Exercised |  | 0 | 0 | 12,125 | 128,062
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Vested |  |  |  | $ 100 | $ 1,500
Employee Service Share-based Compensation, Tax Benefit from Exercise of Equity Instruments Other than Options |  |  |  | $ 100 | $ 600
Restricted Stock [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value |  |  |  | $ 23.56 |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period |  |  |  | 3 years |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total |  | $ 900 |  | $ 900 |
Performance Shares [Member] |  |  |  |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition |  |  |  | 2 years 339 days |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value |  |  |  | $ 24.56 |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period |  |  |  | 5 years |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total |  | $ 2,900 |  | $ 2,900 |
Performance Shares [Member] | Minimum [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period |  |  |  | 3 years |
Performance Shares [Member] | Maximum [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period |  |  |  | 5 years |
Outside Directors [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term |  |  |  | 10 years |
[1] | The expected life in years for awards granted was based on the historical exercise patterns experienced by the Company when the award is made.

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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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 (i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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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 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)(iii)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + 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 (a)(3) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + 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 + Details
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- Definition Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares. + 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 (d)(2) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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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 The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + 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 (d)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Intrinsic value of equity-based compensation awards outstanding. Excludes stock and unit options. + References No definition available. + Details
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- Definition Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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 (f)(2)(i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.D.2) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 + Details
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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 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 + Details
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