Fair Value Measurements (Details) - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Fair Value Measurements
Amount outstanding under revolving credit agreement	$ 0	$ 0
Gains and losses on equity instruments
Net gains recognized during the period on equity investments	115,000
Less: net gains recognized during the period on equity investments sold during the period	59,000
Unrealized gains recognized during the period on equity investments still held at period end	56,000
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value Measurements
Investments	1,322,000	1,182,000
Fair Value, Inputs, Level 1 [Member]
Fair Value Measurements
Investments	$ 1,322,000	$ 1,182,000

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

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Amount of unrealized and realized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=116654751&loc=SL75117546-209714

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Amount of realized gain (loss) from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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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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Fair value portion of contractual arrangement with a lender under which borrowings can be made up to a specific amount at any point in time.

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