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.

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The highest quantity of shares an employee can purchase under the plan per period.

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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.

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Number of options outstanding, including both vested and non-vested options.

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Purchase price of common stock expressed as a percentage of its fair value.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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Stock-Based Compensation Plans - Additional Information (Details) - USD ($)	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Apr. 01, 2018
Employee Stock Purchase Plan
Stock-based compensation plans
Number of shares authorized (in shares)			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	$ 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)	8,307	3,892
2007 Stock Incentive Plan \| Restricted Stock
Stock-based compensation plans
Number of shares authorized (in shares)	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	4 years
2018 Stock Incentive Plan \| Restricted Stock
Stock-based compensation plans
Number of shares authorized (in shares)	800,000
Shares granted to date (in shares)	885,300
Number of shares available for future issuance (in shares)	9,296
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	4 years