Note D - Marketable Equity Securities - Realized Gains on Marketable Equity Securities (Details) - USD ($)	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Sales proceeds	$ 677,000
Cost of securities sold	1,211,000
Equity Securities, FV-NI, Realized Gain (Loss), Total	$ (534,000)	$ 0

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).

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=120269885&loc=SL75117546-209714

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(3)(d))
-URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

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