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Employee Stock Purchase Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant	3,800,000
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum employee subscription rate	15.00%
Maximum employee subscription	$ 25,000
Purchase price of common stock, percent	85.00%
Shares available for grant	834,246
Issuance of common stock under Employee Stock Purchase Plan (Shares)	464,757	314,868	199,464
Proceeds from issuance of shares under incentive and share-based compensation plans, excluding stock options	$ 1,500,000	$ 3,200,000	$ 3,200,000
Risk free interest rate	0.80%	2.30%	1.80%
Dividend yield	0.70%	0.70%	0.40%
Volatility factor of the expected market price of the Company's common stock	166.20%	56.60%	55.90%
Expected life (in years)	6 months	6 months	6 months
Stock-based compensation expense	$ 874,000	$ 1,100,000	$ 1,100,000

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Share-based Compensation Arrangement by Share-based Payment Award, Maximum Employee Subscription

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of cash inflow from issuance of shares under share-based payment arrangement. Excludes option exercised.

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

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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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Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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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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