Note 7 - Equity Incentive Plans (Details Textual) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Share-based Payment Arrangement, Expensed and Capitalized, Amount, Total	$ 6,151	$ 2,242
Service Period Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in shares)	34
Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in shares)	37
Service Period Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)	30
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share)	$ 155.06
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares)	33

The number of grants made 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).

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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).

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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Amount of cost expensed and capitalized for award under share-based payment arrangement.

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

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