Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows From Operating Activities
Net income	$ 112,750,000	$ 91,547,000	$ 86,198,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	81,115,000	79,022,000	74,967,000
Deferred compensation	(2,329,000)	4,857,000	16,805,000
Realized and unrealized gain on long-term investments	2,966,000	(4,178,000)	(152,000)
Stock-based compensation	6,837,000	7,151,000	12,618,000
Deferred income taxes	10,864,000	550,000	(8,426,000)
Other non-cash items	4,622,000	4,857,000	7,334,000
Changes in assets and liabilities, excluding effects of acquisitions:
Receivables, net	5,196,000	(16,358,000)	(17,180,000)
Inventories	(26,832,000)	5,655,000	(3,774,000)
Other current assets	832,000	(489,000)	1,471,000
Accounts payable and accrued liabilities	(19,023,000)	30,476,000	38,261,000
Pension liabilities	(5,065,000)	(1,960,000)	607,000
Environmental and legal liabilities	(478,000)	(1,142,000)	4,561,000
Deferred revenues	(324,000)	(1,125,000)	(1,128,000)
Net Cash Provided By Operating Activities	171,131,000	198,863,000	212,162,000
Cash Flows From Investing Activities
Expenditures for property, plant and equipment	(86,647,000)	(78,613,000)	(103,076,000)
Business acquisitions, net of cash acquired (Note 20)	(22,852,000)	(4,339,000)	(23,510,000)
Other, net	1,684,000	269,000	(3,935,000)
Net Cash Used In Investing Activities	(107,815,000)	(82,683,000)	(130,521,000)
Cash Flows From Financing Activities
Revolving debt and bank overdrafts, net	6,045,000	(6,008,000)	1,292,000
Other debt repayments	(20,714,000)	(20,714,000)	(15,069,000)
Dividends paid	(20,857,000)	(18,907,000)	(17,329,000)
Company stock repurchased	(15,500,000)	(6,000,000)	(2,408,000)
Stock option exercises	4,163,000	3,370,000	4,017,000
Other, net	(4,785,000)	(2,238,000)	(275,000)
Net Cash Used In Financing Activities	(51,648,000)	(50,497,000)	(29,772,000)
Effect of Exchange Rate Changes on Cash	(10,368,000)	7,468,000	(2,269,000)
Net Increase in Cash and Cash Equivalents	1,300,000	73,151,000	49,600,000
Cash and Cash Equivalents at Beginning of Year	298,894,000	225,743,000	176,143,000
Cash and Cash Equivalents at End of Year	300,194,000	298,894,000	225,743,000
Supplemental Cash Flow Information
Cash payments of income taxes, net of refunds	32,973,000	25,661,000	30,581,000
Cash payments of interest	$ 12,829,000	$ 13,889,000	$ 14,730,000