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Equity Incentive Plans and Stock-Based Compensation (Details Textual) | 12 Months Ended
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Dec. 31, 2020 USD ($) plan $ / shares shares | Dec. 31, 2019 USD ($) plan $ / shares shares | Dec. 31, 2018 USD ($) plan $ / shares shares
Option One |  |  |
Stock-Based Compensation |  |  |
Awards, nonvested requisite service period | 60 months |  |
Option Two |  |  |
Stock-Based Compensation |  |  |
Awards, nonvested requisite service period | 48 months |  |
Minimum |  |  |
Stock-Based Compensation |  |  |
Awards, vesting rights (as a percentage) | 0.00% |  |
Maximum |  |  |
Stock-Based Compensation |  |  |
Awards, vesting rights (as a percentage) | 200.00% |  |
Employee stock purchase plan |  |  |
Stock-Based Compensation |  |  |
Number of employee stock purchase plans | plan | 1 | 1 | 1
Minimum number of hours of weekly employment in order to qualify for eligibility in the plan | 20 hours | 20 hours | 20 hours
Minimum number of months of employment in a fiscal year in order to qualify for eligibility in the plan | 5 months | 5 months | 5 months
Offering period (in months) | 6 months | 6 months | 6 months
Percentage of the price at the beginning of the offering period or price at the end of each offering period to derive purchase price | 85.00% | 85.00% | 85.00%
Maximum share value per employee in any calendar year | $ 25,000 | $ 25,000 | $ 25,000
Employee stock purchase plan, shares issued during period | shares | 467,065 | 629,438 | 541,395
Employee stock purchase plan, weighted-average price per share | $ / shares | $ 10.51 | $ 8.53 | $ 9.99
Number of additional shares authorized | shares | 2,000,000 |  |
Shares available for issuance | shares | 3,198,375 |  |
Stock-based compensation | $ 1,500,000 | $ 1,500,000 | $ 1,400,000
Unrecognized compensation cost | $ 700,000 |  |
Unrecognized compensation cost, weighted-average period | 4 months |  |
Options |  |  |
Stock-Based Compensation |  |  |
Options granted | shares | 40,000 | 80,000 | 711,479
Estimated total grant date fair value |  |  | $ 3,000,000.0
Stock-based compensation | $ 600,000 | $ 1,000,000.0 | 1,700,000
Unrecognized compensation cost | $ 1,100,000 |  |
Unrecognized compensation cost, weighted-average period | 2 years 2 months 12 days |  |
Total fair value of options vested | $ 3,300,000 | 6,700,000 | 12,900,000
Nonvested equity stock and stock units |  |  |
Stock-Based Compensation |  |  |
Stock-based compensation | 23,700,000 | $ 23,900,000 | $ 18,600,000
Unrecognized compensation cost | $ 34,500,000 |  |
Unrecognized compensation cost, weighted-average period | 2 years 1 month 6 days |  |
Awards, nonvested grants in period, shares | shares | 1,986,117 | 4,233,701 | 2,978,558
Awards, nonvested requisite service period | 4 years |  |
Awards, nonvested grants in period, fair value | $ 31,000,000.0 | $ 43,000,000.0 | $ 38,100,000
Nonvested equity stock and stock units | Director |  |  |
Stock-Based Compensation |  |  |
Awards, nonvested requisite service period | 1 year |  |

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- Definition Represents the minimum number of hours per week that employees are required to be employed in order to be eligible to participate in the Employee Stock Purchase Plan. + References No definition available. + Details
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- Definition Represents the minimum number of months in a fiscal year that employees are required to be employed in order to be eligible to participate in the Employee Stock Purchase Plan. + References No definition available. + Details
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- Definition Employee Stock Purchase Plan, Percentage of the Price at Beginning of Offering Period or Price at End of Each Offering Period to Derive Purchase Price + References No definition available. + 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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