CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands	Jun. 27, 2020	Dec. 31, 2019
Current Assets
Cash	$ 17,701	$ 35,420
Short-term investments	208,882	129,488
Trade receivables, net	53,653	52,640
Gross inventories (Note 4)	62,580	79,011
Less LIFO reserve	(47,489)	(47,137)
Less excess and obsolescence reserve	(3,025)	(3,573)
Net inventories	12,066	28,301
Prepaid expenses and other current assets	2,637	3,467
Total Current Assets	294,939	249,316
Property, plant and equipment	376,648	372,482
Less allowances for depreciation	(311,103)	(298,568)
Net property, plant and equipment	65,545	73,914
Deferred income taxes	2,260	5,393
Other assets	27,112	20,338
Total Assets	389,856	348,961
Current Liabilities
Trade accounts payable and accrued expenses	40,110	29,771
Contract liabilities with customers (Note 3)	3,646	9,623
Product liability	733	735
Employee compensation and benefits	20,405	14,273
Workers' compensation	5,730	5,619
Income taxes payable	5,689	1,223
Total Current Liabilities	76,313	61,244
Product liability accrual	43	83
Lease liability (Note 5)	1,953	2,176
Contingent liabilities (Note 13)
Stockholders' Equity
Additional paid-in capital	40,085	38,683
Retained earnings	392,859	368,205
Less: Treasury stock - at cost 2020 - 6,709,898 shares 2019 - 6,709,898 shares	(145,590)	(145,590)
Total Stockholders' Equity	311,547	285,458
Total Liabilities and Stockholders' Equity	389,856	348,961
Nonvoting Common Stock [Member]
Stockholders' Equity
Common Stock
Common Stock [Member]
Stockholders' Equity
Common Stock	$ 24,193	$ 24,160