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Stock-Based Compensation Plans - Additional Information (Details) - USD ($) |  | 9 Months Ended |
--- | --- | --- | ---
May 24, 2007 | Sep. 30, 2019 | Sep. 30, 2018 | Apr. 01, 2018
Employee Stock Purchase Plan |  |  |  |
Stock-based compensation plans |  |  |  |
Number of shares authorized |  |  |  | 325,000
Maximum percentage of cash compensation allowed to be deducted for the purchase of common stock by eligible employees |  | 10.00% |  |
Maximum number of shares to be purchased by employee in one calendar year (in shares) |  | 1,000 |  |
Maximum amount of shares to be purchased by employee in one calendar year (in dollars) |  | $ 25,000 |  |
Purchase price expressed as a percentage of the market price of the common stock on the purchase date or on the date of entry |  | 85.00% |  |
Shares issued (in shares) |  | 13,663 | 11,284 |
2007 Stock Incentive Plan | Restricted Stock |  |  |  |
Stock-based compensation plans |  |  |  |
Number of shares authorized |  | 2,800,000 |  |
Stock options outstanding (in shares) |  | 0 |  |
2007 Stock Incentive Plan | Restricted Stock | Minimum |  |  |  |
Stock-based compensation plans |  |  |  |
Vesting period | 1 year |  |  |
2007 Stock Incentive Plan | Restricted Stock | Maximum |  |  |  |
Stock-based compensation plans |  |  |  |
Vesting period | 3 years |  |  |
2018 Stock Incentive Plan | Restricted Stock |  |  |  |
Stock-based compensation plans |  |  |  |
Number of shares authorized |  | 800,000 |  |
Shares granted (in shares) |  | 279,400 |  |
Number of shares available for future issuance (in shares) |  | 613,996 |  |
2018 Stock Incentive Plan | Restricted Stock | Minimum |  |  |  |
Stock-based compensation plans |  |  |  |
Vesting period |  | 1 year |  |
2018 Stock Incentive Plan | Restricted Stock | Maximum |  |  |  |
Stock-based compensation plans |  |  |  |
Vesting period |  | 3 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=116856206&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=116856206&loc=d3e5070-113901 + Details
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- Definition The highest quantity of shares an employee can purchase under the plan per period. + 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=116856206&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=116856206&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=116856206&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=116856206&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=116856206&loc=d3e5070-113901 + Details
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