Note 9 - Share-based Compensation (Details Textual) - USD ($)	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Proceeds from Stock Options Exercised	$ 548,000	$ 0	$ 408,000
Employee Service Share-based Compensation, Tax Benefit Realized from Exercise of Stock Options	337,000	157,000	622,000
Employee Stock Option [Member] \| Selling, General and Administrative Expenses [Member]
Allocated Share-based Compensation Expense	964,000	828,000	707,000
Nonvested [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 1,800,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	2 years 350 days
Nonvested [Member] \| Selling, General and Administrative Expenses [Member]
Allocated Share-based Compensation Expense	$ 966,000	$ 555,000	$ 35,000
Nonvested [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	1 year
Nonvested [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	5 years
The 2001 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	0
The 2001 Equity Incentive Plan [Member] \| Employee Stock Option [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	1 year
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	5 years
The 2001 Equity Incentive Plan [Member] \| Employee Stock Option [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	5 years
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 years
Director Plan 2004 [Member] \| Nonqualified Stock Options [Member] \| Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	1 year
Director Plan 2004 [Member] \| Nonqualified Stock Options [Member] \| Minimum [Member] \| Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	3 years
Director Plan 2004 [Member] \| Nonqualified Stock Options [Member] \| Maximum [Member] \| Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 years
The 2006 Equity Incentive Plan [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	5 years
The 2006 Equity Incentive Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 years
Common Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	315,620	261,306	204,166
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 3.62	$ 3.49	$ 2.14
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	$ 459,000	$ 350,000	$ 1,500,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Period Vested, Aggregate Intrinsic Value	1,600,000	$ 1,400,000	$ 528,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 820,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	2 years 284 days
Common Class A [Member] \| The 2001 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	1,800,000
Share-based Compensation Arrangement by Share-based Payment Award, Options Grants Cumulative	1,683,309
Common Class A [Member] \| Director Plan 2004 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	3,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	1,065,000
Share-based Compensation Arrangement by Share-based Payment Award, Options Grants Cumulative	1,935,000
Common Class A [Member] \| Director Plan 2004 [Member] \| Nonqualified Stock Options [Member] \| Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options Granted at Annual Meeting	36,000
Common Class A [Member] \| The 2006 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	1,800,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	941,085
Share-based Compensation Arrangement by Share-based Payment Award, Options Grants Cumulative	858,915
Common Class A [Member] \| The 2006 Equity Incentive Plan [Member] \| Nonvested [Member]
Stock Issued During Period, Shares, Restricted Stock Award, Gross	20,578	89,416	73,506
Share-based Compensation Arrangement by Share-based Payment Award, Nonvested Restricted Stock, Outstanding Number	174,487
Common Class B [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	52,603	43,551	32,217
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 3.90	$ 5.45	$ 2.16
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	$ 632,000	$ 151,000	$ 502,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Period Vested, Aggregate Intrinsic Value	535,000	$ 415,000	$ 402,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 152,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	2 years 211 days
Common Class B [Member] \| The 2001 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	300,000
Share-based Compensation Arrangement by Share-based Payment Award, Options Grants Cumulative	280,552
Common Class B [Member] \| Director Plan 2004 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	500,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	177,500
Share-based Compensation Arrangement by Share-based Payment Award, Options Grants Cumulative	322,500
Common Class B [Member] \| Director Plan 2004 [Member] \| Nonqualified Stock Options [Member] \| Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options Granted at Annual Meeting	6,000
Common Class B [Member] \| The 2006 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	300,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	157,793
Share-based Compensation Arrangement by Share-based Payment Award, Options Grants Cumulative	142,207
Common Class B [Member] \| The 2006 Equity Incentive Plan [Member] \| Nonvested [Member]
Stock Issued During Period, Shares, Restricted Stock Award, Gross	3,430	14,902	12,251
Share-based Compensation Arrangement by Share-based Payment Award, Nonvested Restricted Stock, Outstanding Number	29,081

Number of nonvested restricted shares outstanding.

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Number of share options (or share units) granted at annual meeting.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of options which vested during the period.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Unrecognized cost of unvested share-based compensation awards.

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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.

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Disclosure of the aggregate tax benefit realized from the exercise of stock options and the conversion of similar instruments during the annual period.

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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.

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

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Total number of shares issued during the period, including shares forfeited, as a result of Restricted Stock Awards.

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