CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 29,427,000	$ 22,450,000
Short-term investments	18,393,000	19,258,000
Accounts receivable	20,235,000	16,445,000
Inventories	49,519,000	50,298,000
Prepaid expenses and other current assets	2,385,000	3,868,000
Total current assets	119,959,000	112,319,000
Long-term investments	40,672,000	46,207,000
Property, plant and equipment	221,342,000	218,912,000
Less accumulated depreciation and amortization	126,451,000	123,977,000
Property, plant and equipment net	94,891,000	94,935,000
Other assets and deferred charges:
Patents	1,391,000	1,421,000
Goodwill	9,730,000	9,730,000
Other	2,200,000	2,278,000
Other assets	13,321,000	13,429,000
Total assets	268,843,000	266,890,000
Current liabilities:
Accounts payable and accrued liabilities	9,925,000	13,200,000
Accrued income and other taxes	852,000	436,000
Total current liabilities	10,777,000	13,636,000
Line of credit	0	0
Other non-current liabilities	13,315,000	12,812,000
Stockholders' equity:
Common stock, par value $0.10 per share; authorized 10,000 shares, issued 3,420 shares	342,000	342,000
Paid-in capital	59,760,000	53,527,000
Retained earnings	342,221,000	337,700,000
Treasury shares,1,592 at March 31, 2021 and 1,594 at December 31, 2020, at cost	(157,572,000)	(151,127,000)
Total stockholders' equity	244,751,000	240,442,000
Total liabilities and stockholders' equity	$ 268,843,000	$ 266,890,000