CONSOLIDATED STATEMENTS OF CASH FLOW (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
OPERATING ACTIVITIES
Net income	$ 40,125	$ 28,005	$ 103,792	$ 65,747
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	15,672	17,436	46,659	52,852
Amortization	1,582	2,366	6,305	7,571
Change in deferred taxes and other liabilities	13,548	1,199	12,802	(7,012)
Provision for write-off of property, plant and equipment	(5)	2,131	1,101	3,255
Non-cash interest expense	151	150	454	304
Compensation and benefits paid or payable in Class A Common Stock	790	543	1,413	1,879
Fair value adjustment on foreign currency option		(10)		61
Changes in operating assets and liabilities that provided cash:
Accounts receivable	(9,950)	(2,813)	(7,140)	(39,954)
Contract assets	(9,605)	3,040	(6,558)	(8,721)
Inventories	(3,760)	(2,968)	(21,927)	(16,408)
Prepaid expenses and other current assets	131	103	(4,057)	(5,117)
Income taxes prepaid and receivable	304	(551)	662	(454)
Accounts payable	363	(2,728)	7,837	6,154
Accrued liabilities	3,407	7,552	(8,762)	12,171
Income taxes payable	(5,611)	6,766	1,619	13,355
Noncurrent receivables	(339)	(4,676)	(679)	(8,846)
Other noncurrent liabilities	(2,251)	(5,102)	(4,411)	(6,333)
Other, net	(1,055)	(5,728)	(2,517)	(9,049)
Net cash provided by operating activities	43,497	44,715	126,593	61,455
INVESTING ACTIVITIES
Purchases of property, plant and equipment	(13,442)	(21,441)	(48,846)	(60,564)
Purchased software	(257)	(78)	(306)	(130)
Net cash used in investing activities	(13,699)	(21,519)	(49,152)	(60,694)
FINANCING ACTIVITIES
Proceeds from borrowings		3,000	20,000	26,031
Principal payments on debt	(58,006)	(10,471)	(95,014)	(24,614)
Principal payments on finance lease liabilities	(298)		(876)
Taxes paid in lieu of share issuance			(971)	(1,652)
Proceeds from options exercised	33	52	105	202
Dividends paid	(5,814)	(5,485)	(17,435)	(16,441)
Net cash used in financing activities	(64,085)	(12,904)	(94,191)	(16,474)
Effect of exchange rate changes on cash and cash equivalents	(7,207)	(4,443)	(7,266)	(7,421)
(Decrease)/increase in cash and cash equivalents	(41,494)	5,849	(24,016)	(23,134)
Cash and cash equivalents at beginning of period	215,233	154,744	197,755	183,727
Cash and cash equivalents at end of period	$ 173,739	$ 160,593	$ 173,739	$ 160,593