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The maximum number of equity awards an employee may receive as a percentage of the target number.

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Represents the intrinsic value for stock purchased under the employee stock purchase plan.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cash inflow from issuance of shares under share-based payment arrangement. Excludes option exercised.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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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 estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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Number of additional shares authorized for issuance under share-based payment arrangement.

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Number of shares authorized for issuance under share-based payment arrangement.

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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.

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Price of a single share of a number of saleable stocks of a company.

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Percentage of vesting of award under share-based payment arrangement.

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Intrinsic value of outstanding award under share-based payment arrangement. Excludes share and unit options.

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Intrinsic value of vested award under share-based payment arrangement. Excludes share and unit options.

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Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Note 3 - Stock-based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended		3 Months Ended		6 Months Ended
	Jun. 11, 2020	Feb. 29, 2020	Feb. 28, 2018	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Nov. 13, 2014
Proceeds, Issuance of Shares, Share-based Payment Arrangement, Excluding Option Exercised						$ 14,110	$ 12,471
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)						453,000
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)						$ 171.47
Proceeds from Stock Plans						$ 1,892	1,627
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Vested				$ 39,700	$ 26,300	221,900	84,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding				$ 721,300		$ 721,300
Share Price (in dollars per share)				$ 237.00		$ 237.00
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total				$ 135,800		$ 135,800
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)						3 years
Proceeds, Issuance of Shares, Share-based Payment Arrangement, Excluding Option Exercised						$ 14,100	$ 12,500
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)						70,000
Time-Based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)						70,000
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)						$ 181.41
Time-Based RSUs [Member] \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)						4 years
Time-Based RSUs [Member] \| Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)						1 year
PSU 2020 [Member]
Share Price (in dollars per share)		$ 182.62
Share-based Compensation Arrangement by Share-based Payment Award, Price Per Share Payable Upon Vesting of Equity Instruments Other than Options (in dollars per share)		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)		$ 182.62
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term (Year)		2 years
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate		33.60%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate		1.40%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate		1.10%
PSU 2020 [Member] \| Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)		100,000
Share-based Compensation Arrangement by Share-based Payment Award, Vesting, Measurement Period of Relative Revenue Growth Rate to Industry Average (Year)		2 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Maximum Percentage Allowed		300.00%
Maximum Stock Compensation Costs		$ 51,100
PSU 2020 [Member] \| Executive Officer [Member] \| Vesting First Quarter of 2022 if Performance Conditions are Met [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		50.00%
PSU 2020 [Member] \| Executive Officer [Member] \| Vesting Over Two Years Following First Quarter of 2022 on Quarterly Basis [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		50.00%
PSU 2020 [Member] \| Non-Executive Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)		30,000
Share-based Compensation Arrangement by Share-based Payment Award, Vesting, Measurement Period of Relative Revenue Growth Rate to Industry Average (Year)		2 years
Maximum Stock Compensation Costs		$ 12,900
PSU 2020 [Member] \| Non-Executive Employees [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Minimum Percentage Allowed		200.00%
PSU 2020 [Member] \| Non-Executive Employees [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Maximum Percentage Allowed		300.00%
PSU 2020 [Member] \| Non-Executive Employees [Member] \| Vesting First Quarter of 2020 if Performance Conditions are Met [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		50.00%
PSU 2020 [Member] \| Non-Executive Employees [Member] \| Vesting Over Two Years Following First Quarter of 2022 on Quarterly Basis [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		50.00%
PSU 2018 [Member] \| Non-Executive Employees [Member] \| Annual or Quarterly Vesting of Awards Not Based on Performance [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)			2 years
The2014 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)								5,500,000
Amended and Restated 2014 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized (in shares)	10,500,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)				6,200,000		6,200,000
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)				4,500,000		4,500,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total				$ 100		$ 100
Stock Issued During Period, Shares, Employee Stock Purchase Plans (in shares)				0	0	15,000	14,000
Employee Stock Purchase Plan Shares Issued, Intrinsic Value						$ 1,000	$ 300
Proceeds from Stock Plans						$ 1,900	$ 1,600