Note 15 - Share Plans (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Feb. 10, 2010
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized				9,100,000
Allocated Share-based Compensation Expense, Total	$ 14,563	$ 10,205	$ 9,493
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	$ 43.88	$ 40.13	$ 33.24
Proceeds from Stock Options Exercised	$ 5,614	$ 6,951	$ 1,623
Payments Related to Tax Withholding for Share-based Compensation	$ 5,659	$ 5,892	$ 14,008
Board of Directors Chairman [Member]
Deferred Compensation Arrangement with Individual, Shares Issued	33,419	34,095	19,326
Deferred Compensation Arrangement with Individual, Shares Vested	33,419	22,762	19,326
Deferred Compensation Arrangement with Individual, Compensation Expense	$ 1,718	$ 1,133	$ 670
Employee Stock Option [Member]
Allocated Share-based Compensation Expense, Total	$ 4,998	$ 4,503	$ 4,366
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	4 years
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 years
Shares Paid for Tax Withholding for Share Based Compensation	63,817	9,033	473,743
Proceeds from Stock Options Exercised	$ 5,614	$ 6,951	$ 1,623
Payments Related to Tax Withholding for Share-based Compensation	3,846	$ 4,301	$ 13,056
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total	$ 9,538
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	2 years 182 days
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
Shares Paid for Tax Withholding for Share Based Compensation	38,186	39,500	28,593
Payments Related to Tax Withholding for Share-based Compensation	$ 1,812	$ 1,591	$ 952
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total	$ 9,210
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year 292 days
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Performance Measurement, Period	3 years
Restricted Stock and Performance Shares [Member]
Allocated Share-based Compensation Expense, Total	$ 9,565	$ 5,702	$ 5,127
Minimum [Member]
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	$ 43.88	$ 40.12	$ 33.23
Performance Share Award, Percentage	0.00%
Maximum [Member]
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	$ 45.29	$ 48.98	$ 35.37
Performance Share Award, Percentage	200.00%

Number of shares vested during the period pursuant to the terms of a deferred compensation arrangement.

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The percentage of the target performance share award.

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Period of performance measurement for share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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Number of shares issued pursuant to the terms of a deferred compensation arrangement.

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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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Amount of cash outflow to satisfy an employee's income tax withholding obligation as part of a net-share settlement of a share-based award.

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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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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.

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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).

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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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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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For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer.

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