Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING ACTIVITIES
Net income	$ 97,243	$ 133,383	$ 83,019
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	63,328	62,085	68,800
Amortization	9,377	8,710	10,236
Change in deferred taxes and other liabilities	11,101	13,702	8,972
Provision for write-off of property, plant and equipment	1,173	3,119	3,707
Non-cash interest (income)/expense	(290)	605	459
Write-off of pension liability adjustments due to settlement/curtailment	411	450	1,494
Compensation and benefits paid or payable in Class A Common Stock	1,505	2,063	2,203
Provision for credit losses from uncollected receivables and contract assets	1,628	309	579
Foreign currency remeasurement (gain)/loss on intercompany loans	14,246	(3,730)	(1,611)
Changes in operating assets and liabilities that provided/(used) cash:
Accounts receivable	31,522	9,278	(19,718)
Contract assets	(59,122)	(19,199)	(10,267)
Inventories	(13,685)	(8,923)	(968)
Prepaid expenses and other current assets	(7,811)	(2,291)	(5,815)
Income taxes prepaid and receivable	113	1,390	(1,402)
Accounts payable	(15,586)	10,524	9,340
Accrued liabilities	(3,856)	(7,393)	8,209
Income taxes payable	5,939	3,979	(824)
Noncurrent receivables	4,158	(1,341)	(12,249)
Other noncurrent liabilities	(2,437)	(6,573)	(5,479)
Other, net	1,296	205	(6,200)
Net cash provided by operating activities	140,253	200,352	132,485
INVESTING ACTIVITIES
Purchase of business, net of cash acquired	0	(30,793)	0
Purchases of property, plant and equipment	(41,463)	(67,358)	(81,579)
Purchased software	(927)	(597)	(1,307)
Net cash used in investing activities	(42,390)	(98,748)	(82,886)
FINANCING ACTIVITIES
Proceeds from borrowings	75,000	45,000	26,031
Principal payments on debt	(101,020)	(120,017)	(29,913)
Principal payments on finance lease liabilities	(7,214)	(1,180)	0
Debt acquisition costs	(2,432)	0	0
Taxes paid in lieu of share issuance	(490)	(971)	(1,652)
Proceeds from options exercised	55	112	202
Dividends paid	(24,568)	(23,251)	(21,926)
Net cash used in financing activities	(60,669)	(100,307)	(27,258)
Effect of exchange rate changes on cash and cash equivalents	8,582	(3,512)	(8,313)
Increase/(decrease) in cash and cash equivalents	45,776	(2,215)	14,028
Cash and cash equivalents at beginning of period	195,540	197,755	183,727
Cash and cash equivalents at end of period	$ 241,316	$ 195,540	$ 197,755