Summary Of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

Summary Of Significant Accounting Policies [Abstract]

Summary Of The Amortized Costs And Fair Values Of Marketable Securities

	(In thousands)
	MARKETABLE SECURITIES
	Amortized Cost		Fair Value		Gross Unrealized Gains		Gross Unrealized Losses
December 31, 2019
Tax-exempt Municipal Bonds	$	39,313	$	39,484	$	176	$	5
Variable Rate Demand Notes		39,249		39,249		-		-
Total Marketable Securities	$	78,562	$	78,733	$	176	$	5
December 31, 2018
Tax-exempt Municipal Bonds	$	40,156	$	40,182	$	44	$	18
Variable Rate Demand Notes		94,416		94,416		-		-
Total Marketable Securities	$	134,572	$	134,598	$	44	$	18

Schedule Of Changes In Product Warranty

	(In thousands)
	Year Ended December 31
	2019		2018
Beginning balance January 1	$	221	$	383
Accruals during the period		416		315
Charges / payments made under the warranties		(374)		(477)
Balance December 31	$	263	$	221