CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities:
Net income	$ 49,990	$ 47,319	$ 87,651
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	71,425	49,162	50,073
Equity compensation expense	13,532	12,305	11,223
Deferred income taxes	(13,406)	(17,549)	(3,325)
Equity in undistributed income of unconsolidated joint ventures	(4,877)	(5,319)	(5,501)
Dividends received from unconsolidated joint ventures	7,075	5,375	4,431
Pension settlement charges	(63)	53,213	0
Pension and other postretirement benefits	(160)	(943)	(1,552)
Asbestos-related charges	(682)	1,720	704
Loss (gain) on sale or disposal of property, plant and equipment	41	756	(164)
Impairment charges	639	1,537	1,506
Provision (benefit) for credit losses	223	437	236
Changes in assets and liabilities:
Accounts receivable	(8,934)	20,677	(3,824)
Contract assets	(4,120)	273	(22,728)
Inventories	34,687	(1,200)	(19,013)
Pension and postretirement benefit contributions	(253)	(103)	(25,354)
Other current assets	(217)	(1,519)	(648)
Accounts payable and other accrued expenses	10,084	(9,139)	(7,886)
Other, net	10,072	4,321	991
Net cash provided by operating activities	165,056	161,323	66,820
Investing Activities:
Acquisition of business, net of cash received	0	0	(77,969)
Isola asset acquisition	0	0	(43,434)
Capital expenditures	(40,385)	(51,597)	(47,115)
Proceeds from the sale of property, plant and equipment, net	0	9	1,081
Return of capital from unconsolidated joint ventures	0	2,625	0
Net cash used in investing activities	(40,385)	(48,963)	(167,437)
Financing Activities:
Proceeds from borrowings under revolving credit facility	150,000	0	102,500
Line of credit issuance costs	(1,862)	0	0
Repayment of debt principal and finance lease obligations	(248,330)	(105,886)	(6,162)
Payments of taxes related to net share settlement of equity awards	(5,357)	(7,550)	(6,600)
Proceeds from the exercise of stock options, net	0	344	861
Proceeds from issuance of shares to employee stock purchase plan	1,360	1,249	1,082
Share repurchases	0	0	(2,999)
Net cash (used in) provided by financing activities	(104,189)	(111,843)	88,682
Effect of exchange rate fluctuations on cash	4,454	(1,406)	(1,486)
Net decrease in cash and cash equivalents	24,936	(889)	(13,421)
Cash and cash equivalents at beginning of period	166,849	167,738	181,159
Cash and cash equivalents at end of period	191,785	166,849	167,738
Supplemental Disclosures:
Accrued capital additions	715	3,420	2,744
Interest, net of amounts capitalized	7,251	7,762	7,040
Income taxes	$ 29,983	$ 17,593	$ 29,161