Note 5 - Share-based Compensation (Details Textual)	3 Months Ended
Mar. 31, 2018 USD ($) shares
Common Class A Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	74,516
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	74,516
Common Class A [Member] \| Employee Stock Option [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total \| $	$ 1,600,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	3 years 255 days
Common Class A [Member] \| Nonvested [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total \| $	$ 740,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	2 years 332 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
Common Class A [Member] \| Director Plan 2004 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	3,000,000
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
Common Class B [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross
Common Class B [Member] \| Employee Stock Option [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total \| $	$ 119,000
Common Class B [Member] \| Nonvested [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total \| $	$ 222,000
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
Common Class B [Member] \| Director Plan 2004 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	500,000
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

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

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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ 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

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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

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, 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
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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
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- Definition

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

+ References

No definition available.

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- Definition

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.

+ References

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