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Note 13 - Stock-based Compensation - Information about Stock Options Outstanding (Details) - $ / shares | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Options outstanding, vested and expected to vest, number outstanding (in shares) | 252,616 | 399,055 | 569,639 | 766,042
Options outstanding, vested and expected to vest, weighted average exercise price (in dollars per share) | $ 64.71 | $ 51.13 | $ 45 | $ 36.52
Exercise Price Range One [Member] |  |  |  |
Range of exercise prices, lower limit (in dollars per share) | 3.67 |  |  |
Range of exercise prices, upper limit (in dollars per share) | $ 31.43 |  |  |
Options outstanding, vested and expected to vest, number outstanding (in shares) | 30,972 |  |  |
Options outstanding, vested and expected to vest, weighted average remaining contractual life (Year) | 2 years 346 days |  |  |
Options outstanding, vested and expected to vest, weighted average exercise price (in dollars per share) | $ 24.59 |  |  |
Options exercisable, number exercisable (in shares) | 30,972 |  |  |
Options exercisable, weighted average exercise price (in dollars per share) | $ 24.59 |  |  |
Exercise Price Range Two [Member] |  |  |  |
Range of exercise prices, lower limit (in dollars per share) | 31.44 |  |  |
Range of exercise prices, upper limit (in dollars per share) | $ 66.87 |  |  |
Options outstanding, vested and expected to vest, number outstanding (in shares) | 133,492 |  |  |
Options outstanding, vested and expected to vest, weighted average remaining contractual life (Year) | 5 years 131 days |  |  |
Options outstanding, vested and expected to vest, weighted average exercise price (in dollars per share) | $ 58.52 |  |  |
Options exercisable, number exercisable (in shares) | 69,210 |  |  |
Options exercisable, weighted average exercise price (in dollars per share) | $ 58.78 |  |  |
Exercise Price Range Three [Member] |  |  |  |
Range of exercise prices, lower limit (in dollars per share) | 66.88 |  |  |
Range of exercise prices, upper limit (in dollars per share) | $ 96.20 |  |  |
Options outstanding, vested and expected to vest, number outstanding (in shares) | 51,894 |  |  |
Options outstanding, vested and expected to vest, weighted average remaining contractual life (Year) | 5 years 200 days |  |  |
Options outstanding, vested and expected to vest, weighted average exercise price (in dollars per share) | $ 72.49 |  |  |
Options exercisable, number exercisable (in shares) | 25,743 |  |  |
Options exercisable, weighted average exercise price (in dollars per share) | $ 71.73 |  |  |
Exercise Price Range Four [Member] |  |  |  |
Range of exercise prices, lower limit (in dollars per share) | 96.21 |  |  |
Range of exercise prices, upper limit (in dollars per share) | $ 123.10 |  |  |
Options outstanding, vested and expected to vest, number outstanding (in shares) | 36,258 |  |  |
Options outstanding, vested and expected to vest, weighted average remaining contractual life (Year) | 9 years 83 days |  |  |
Options outstanding, vested and expected to vest, weighted average exercise price (in dollars per share) | $ 110.59 |  |  |
Options exercisable, number exercisable (in shares) | 0 |  |  |
Options exercisable, weighted average exercise price (in dollars per share) | $ 0 |  |  |

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- Definition Number of options outstanding, including both vested and non-vested options. + 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 -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan. + 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 (c)(1)(i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range. + 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 (g) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The number of shares reserved for issuance pertaining to the outstanding exercisable stock options as of the balance sheet date in the customized range of exercise prices for which the market and performance vesting condition has been satisfied. + 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 (c)(iii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range. + 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 (g) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur. + 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 (e)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Weighted average exercise price as of the balance sheet date for those equity-based payment arrangements exercisable and outstanding. + 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 (c)(1)(iii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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