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Note 8 - Stock-based Compensation (Details Textual) - USD ($) $ / shares in Units, shares in Thousands | 1 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Dec. 31, 2019 | Dec. 31, 2014 | Aug. 31, 2013 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Share-based Payment Arrangement, Expense |  |  |  | $ 14,794,000 | $ 17,719,000 | $ 9,396,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares) |  |  |  | 10,471 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share) |  |  |  | $ 4.69 |  |  |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total |  |  |  | $ 56,094,000 |  |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Expected to be Recognized Next Year |  |  |  | 17,758,000 |  |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Expected to be Recognized Year Two |  |  |  | 16,281,000 |  |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Expected to be Recognized Year Three |  |  |  | 12,484,000 |  |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Expected to be Recognized Year Four |  |  |  | 9,571,000 |  |  |
Incentive Plan [Member] |  |  |  |  |  |  |
Share-based Payment Arrangement, Expense |  |  |  | $ 12,938,000 | $ 17,164,000 | $ 9,223,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share) |  |  |  | $ 5.48 | $ 2.63 | $ 4.92 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value |  |  |  | $ 1,562,000 | $ 1,127,000 | $ 4,504,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares) | 968 |  |  | 4,592 | 968 | 805 | 468
Incentive Plan [Member] | Share-based Payment Arrangement, Option [Member] | Maximum [Member] |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term (Year) |  |  |  | 10 years |  |  |
Incentive Plan [Member] | Share-based Payment Arrangement, Option [Member] | Vest 25% Each Year Until Fully Vested [Member] |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage |  |  |  | 25.00% |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year) |  |  |  | 4 years |  |  |
Incentive Plan [Member] | Performance Shares [Member] | August 2013 [Member] |  |  |  |  |  |  |
Share-based Payment Arrangement, Expense |  |  |  | $ 1,768,000 |  |  |
Incentive Plan [Member] | Performance Shares [Member] | December 2019 [Member] |  |  |  |  |  |  |
Share-based Payment Arrangement, Expense |  |  |  | $ 684,000 |  |  |
Incentive Plan [Member] | Performance Shares [Member] | Vest Upon Successful Completion of Specific Development Milestones [Member] |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares) | 315 | 1,250 | 1,032 |  |  |  |
Incentive Plan [Member] | Performance Shares [Member] | Vest Upon Successful Completion of Specific Development Milestones [Member] | August 2013 [Member] |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage |  |  |  | 100.00% |  |  |
Incentive Plan [Member] | Performance Shares [Member] | Vest Upon Successful Completion of Specific Development Milestones [Member] | December 2014 [Member] |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage |  |  |  | 85.00% |  |  |
Incentive Plan [Member] | Performance Shares [Member] | Vest Upon Successful Completion of Specific Development Milestones [Member] | December 2019 [Member] |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage |  |  |  | 100.00% |  |  |
Inducement Plan [Member] |  |  |  |  |  |  |
Share-based Payment Arrangement, Expense |  |  |  | $ 1,494,000 | $ 323,000 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year) |  |  |  | 4 years |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term (Year) |  |  |  | 5 years 3 months 18 days |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share) |  |  |  | $ 2.73 | $ 2.41 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year) |  |  |  | 10 years |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value |  |  |  | $ 0 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value |  |  |  | $ 29,716,000 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares) | 171 |  |  | 229 | 171 |  |
Inducement Plan [Member] | Vest 25% Each Year Until Fully Vested [Member] |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage |  |  |  | 25.00% |  |  |
Inducement Plan [Member] | Share-based Payment Arrangement, Option [Member] |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate |  |  |  | 0.00% |  |  |
Employee Stock Purchase Plan [Member] |  |  |  |  |  |  |
Share-based Payment Arrangement, Expense |  |  |  | $ 362,000 | $ 232,000 | $ 173,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares) |  |  |  | 4,475 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares) |  |  |  | 2,873 |  |  |
Percentage of Salary to Purchase Common Stock, Maximum |  |  |  | 15.00% |  |  |
Percentage of Common Stock Shares, Beginning |  |  |  | 85.00% |  |  |
Percentage of Common Stock Shares, Ending |  |  |  | 85.00% |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Number of Shares Per Employee (in shares) |  |  |  | 3 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Number of Shares Per Employee, Amount |  |  |  | $ 25,000 |  |  |
Stock Issued During Period, Shares, Employee Stock Purchase Plans (in shares) |  |  |  | 246 | 115 | 92 |
Employee Stock Ownership Plan (ESOP), Weighted Average Purchase Price of Shares Purchased (in dollars per share) |  |  |  | $ 2.56 | $ 3.51 | $ 3.83 |
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) |  |  |  | $ 1.47 | $ 2.01 | $ 1.89 |
Incentive Plan and Inducement Plan [Member] |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate |  |  |  | 0.00% | 0.00% | 0.00% |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value |  |  |  | $ 18,739 | $ 12,499,000 | $ 8,952,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number (in shares) |  |  |  | 26,487 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price (in dollars per share) |  |  |  | $ 6.13 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term (Year) |  |  |  | 7 years 4 months 24 days |  |  |

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- Definition 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. + 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 (a)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition 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). + 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)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition 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. + 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=120381028&loc=d3e5070-113901 + Details
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- Definition Gross number of share options (or share units) granted during the period. + References No definition available. + Details
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- Definition Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. 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=120381028&loc=d3e5070-113901 + Details
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- Definition Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. 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=120381028&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=120381028&loc=d3e5070-113901 + Details
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