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Equity Incentive Plans and Stock-Based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Employee stock purchase plan |  |  |  |
Stock-based compensation |  |  |  |
Employee stock purchase plan, shares issued during period |  |  | 263,933 | 277,838
Employee stock purchase plan, weighted-average price per share |  |  | $ 11.58 | $ 10.51
Shares available for issuance | 2,900,000 |  | 2,900,000 |
Discount from market price specific date |  |  | 15.00% |
Stock-based compensation expense | $ 0.2 | $ 0.2 | $ 0.8 | $ 0.7
Unrecognized compensation cost | 0.4 |  | $ 0.4 |
Unrecognized compensation cost, weighted-average period |  |  | 4 months |
Options |  |  |  |
Stock-based compensation |  |  |  |
Stock-based compensation expense | 0.1 | 0.1 | $ 0.2 | 0.3
Unrecognized compensation cost | 0.7 |  | $ 0.7 |
Unrecognized compensation cost, weighted-average period |  |  | 1 year 7 months 6 days |
Nonvested equity stock units and stock units |  |  |  |
Stock-based compensation |  |  |  |
Stock-based compensation expense | 7.0 | $ 6.3 | $ 12.9 | $ 11.8
Unrecognized compensation cost | $ 51.5 |  | $ 51.5 |
Unrecognized compensation cost, weighted-average period |  |  | 2 years 3 months 18 days |
Awards, nonvested grants in period, shares | 100,000 | 100,000 | 1,998,321 | 1,900,000
Awards, nonvested requisite service period |  |  | 4 years |
Awards, nonvested grants in period, fair value | $ 2.8 | $ 1.7 | $ 41.3 | $ 29.3
Nonvested equity stock units and stock units | Director |  |  |  |
Stock-based compensation |  |  |  |
Awards, nonvested requisite service period |  |  | 1 year |
Nonvested equity stock units and stock units | Minimum |  |  |  |
Stock-based compensation |  |  |  |
Awards, vesting rights (as a percentage) |  |  | 0.00% |
Nonvested equity stock units and stock units | Maximum |  |  |  |
Stock-based compensation |  |  |  |
Awards, vesting rights (as a percentage) |  |  | 200.00% |

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- Definition The discount rate from market value on specific date that participants pay for shares. + References No definition available. + Details
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- Definition Represents the total fair value of nonvested equity stock units granted during the period. + References No definition available. + Details
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- Definition Amount of expense for award under share-based payment arrangement. Excludes amount capitalized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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 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). + 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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