Marketable Securities - Schedule for Marketable Securities (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Available-for-sale securities:
Amortized Cost	$ 13,257,000	$ 22,992,000
Gross Unrealized Gain	2,000	2,000
Gross Unrealized (Losses)	(223,000)	(715,000)
Estimated Fair Value	13,036,000	22,279,000
Held-to-maturity securities:
Amortized Cost		0
Tax-exempt municipal securities
Available-for-sale securities:
Amortized Cost	10,055,000	15,852,000
Gross Unrealized Gain	2,000	2,000
Gross Unrealized (Losses)	(144,000)	(507,000)
Estimated Fair Value	9,913,000	15,347,000
Corporate debt securities
Available-for-sale securities:
Amortized Cost	3,202,000	7,140,000
Gross Unrealized Gain	0	0
Gross Unrealized (Losses)	(79,000)	(208,000)
Estimated Fair Value	3,123,000	$ 6,932,000
Term deposits
Held-to-maturity securities:
Amortized Cost	27,175,000
Gross Unrealized Gain	0
Gross Unrealized (Losses)	0
Estimated Fair Value	$ 27,175,000