Marketable Securities - Available-For-Sale Securities (Details) - USD ($)	Mar. 31, 2023	Dec. 31, 2022
Available-for-sale securities:
Amortized Cost	$ 21,030,000	$ 22,992,000
Gross Unrealized Gain	2,000	2,000
Gross Unrealized (Losses)	(570,000)	(715,000)
Estimated Fair Value	20,462,000	22,279,000
Held-to-maturity securities:
Amortized Cost		0
Tax-exempt municipal securities
Available-for-sale securities:
Amortized Cost	14,793,000	15,852,000
Gross Unrealized Gain	2,000	2,000
Gross Unrealized (Losses)	(400,000)	(507,000)
Estimated Fair Value	14,395,000	15,347,000
Corporate debt securities
Available-for-sale securities:
Amortized Cost	6,237,000	7,140,000
Gross Unrealized Gain	0	0
Gross Unrealized (Losses)	(170,000)	(208,000)
Estimated Fair Value	6,067,000	$ 6,932,000
Term deposits
Held-to-maturity securities:
Amortized Cost	16,727,000
Gross Unrealized Gain	0
Gross Unrealized (Losses)	0
Estimated Fair Value	$ 16,727,000

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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