CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating Activities
Consolidated net income	$ 76,269,000	$ 70,254,000	$ 69,886,000
Adjustments to reconcile income (loss) from continuing operations to net cash provided by operating activities:
Depreciation, depletion and amortization	51,209,000	58,223,000	63,981,000
Loss on disposal of property, plant and equipment	1,093,000	288,000	941,000
Deferred income taxes	1,257,000	1,250,000	1,772,000
Provision for bad debts	1,011,000	878,000	49,000
Stock-based compensation	5,476,000	7,237,000	5,860,000
Other non-cash items	612,000	41,000	189,000
Changes in operating assets and liabilities
Accounts receivable	537,000	(14,186,000)	(7,577,000)
Inventories	6,675,000	(7,340,000)	(3,713,000)
Prepaid expenses and other current assets	3,398,000	(5,787,000)	3,164,000
Pension plan funding	(16,963,000)	(6,650,000)	(8,466,000)
Accounts payable	(5,231,000)	24,824,000	6,351,000
Restructuring liabilities	(1,103,000)	(2,550,000)	(4,741,000)
Income taxes payable	3,748,000	(712,000)	6,829,000
Tax benefits related to stock incentive programs	513,000	166,000	136,000
Other	11,417,000	7,723,000	7,758,000
Net cash provided by operations	139,918,000	133,659,000	142,419,000
Investing Activities
Purchases of property, plant and equipment	(52,130,000)	(52,060,000)	(34,518,000)
Purchases of short-term investments	(5,390,000)	(12,423,000)	(10,738,000)
Proceeds from sales of short-term investments	9,310,000	9,380,000	4,125,000
Proceeds from disposal of property, plant and equipment	169,000	78,000	39,000
Net cash used in investing activities	(48,041,000)	(55,025,000)	(41,092,000)
Financing Activities
Repayment of long-term debt	(8,558,000)	(275,000)	(4,600,000)
Proceeds from issuance of long term debt	0	1,596,000	0
Net issuance (repayment) of short-term debt	1,031,000	2,030,000	(1,331,000)
Purchase of common shares for treasury	(25,884,000)	(48,004,000)	(27,922,000)
Cash dividends paid	(4,409,000)	(3,601,000)	(3,720,000)
Proceeds from issuance of stock under option plan	8,173,000	5,912,000	1,086,000
Excess tax benefits related to stock incentive programs	313,000	6,000	53,000
Dividends to non-controlling shareholders	(4,645,000)	0	0
Net cash used in financing activities	(33,979,000)	(42,336,000)	(36,434,000)
Effect of exchange rate changes on cash and cash equivalents	1,042,000	(8,973,000)	(8,012,000)
Net increase in cash and cash equivalents	58,940,000	27,325,000	56,881,000
Cash and cash equivalents at beginning of period	395,152,000	367,827,000	310,946,000
Cash and cash equivalents at end of period	454,092,000	395,152,000	367,827,000
Non-cash Investing and Financing Activities:
Treasury stock purchases settled after year-end	$ 1,771,000	$ 0	$ 2,069,000