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Stock-Based Compensation Plans - 2007 Stock Incentive Plan (Details) - shares | 12 Months Ended |  |
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Dec. 31, 2020 | May 31, 2018 | May 31, 2007
2007 Stock Incentive Plan |  |  |
Stock-based compensation plans |  |  |
Number of shares authorized (in shares) |  |  | 2,800,000
2018 Stock Incentive Plan |  |  |
Stock-based compensation plans |  |  |
Number of shares authorized (in shares) |  | 800,000 |
Restricted Stock | 2018 Stock Incentive Plan |  |  |
Stock-based compensation plans |  |  |
Number of shares awarded (in shares) | 598,750 |  |
Number of shares available (in shares) | 295,846 |  |
Equity Options | 2007 Stock Incentive Plan |  |  |
Stock-based compensation plans |  |  |
Stock options outstanding (in shares) | 0 |  |
Minimum | 2007 Stock Incentive Plan |  |  |
Stock-based compensation plans |  |  |
Vesting period | 1 year |  |
Minimum | 2018 Stock Incentive Plan |  |  |
Stock-based compensation plans |  |  |
Vesting period | 1 year |  |
Maximum | 2007 Stock Incentive Plan |  |  |
Stock-based compensation plans |  |  |
Vesting period | 4 years |  |
Maximum | 2018 Stock Incentive Plan |  |  |
Stock-based compensation plans |  |  |
Vesting period | 4 years |  |

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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 Number of shares authorized for issuance under share-based payment arrangement. + 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)(3) -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 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=120381028&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=120381028&loc=d3e5070-113901 + Details
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