Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract]
Net income	$ 27,609	$ 7,594
Adjustments to reconcile net income to net cash provided by/(used in) operating activities:
Depreciation	16,589	15,506
Amortization	2,293	2,564
Change in deferred taxes and other liabilities	4,442	5,817
Impairment of property, plant and equipment	185	197
Non-cash interest expense	45	151
Compensation and benefits paid or payable in Class A Common Stock	(13)	(682)
Provision for credit losses from uncollected receivables and contract assets	(110)	1,655
Foreign currency remeasurement (gain)/loss on intercompany loans	(308)	15,387
Fair value adjustment on foreign currency options	139	64
Changes in operating assets and liabilities that provided/(used) cash:
Accounts receivable	(3,236)	(3,394)
Contract assets	16,104	(8,840)
Inventories	(8,563)	(19,750)
Prepaid expenses and other current assets	(899)	(2,156)
Income taxes prepaid and receivable	(1,465)	(237)
Accounts payable	9,188	(1,046)
Accrued liabilities	(19,485)	(15,072)
Income taxes payable	(8,077)	(3,571)
Noncurrent receivables	488	(231)
Other noncurrent liabilities	(2,097)	(60)
Other, net	857	(534)
Net cash provided by/(used in) operating activities	33,686	(6,638)
INVESTING ACTIVITIES
Purchases of property, plant and equipment	(12,534)	(12,759)
Purchased software	(2)	(46)
Net cash used in investing activities	(12,536)	(12,805)
FINANCING ACTIVITIES
Proceeds from borrowings	8,000	70,000
Principal payments on debt	(22,007)	(3,006)
Principal payments on finance lease liabilities	(349)	(6,134)
Taxes paid in lieu of share issuance	(998)	(490)
Proceeds from options exercised	128	0
Dividends paid	(6,468)	(6,139)
Net cash (used in)/provided by financing activities	(21,694)	54,231
Effect of exchange rate changes on cash and cash equivalents	(2,901)	(7,648)
(Decrease)/increase in cash and cash equivalents	(3,445)	27,140
Cash and cash equivalents at beginning of period	241,316	195,540
Cash and cash equivalents at end of period	$ 237,871	$ 222,680