CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
OPERATING ACTIVITIES
Net income	$ 28,484	$ 15,220	$ 69,272	$ 27,427
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	17,436	15,522	52,852	45,367
Amortization	2,366	2,608	7,571	7,889
Change in other noncurrent liabilities	(5,102)	(168)	(6,333)	(2,522)
Change in deferred taxes and other liabilities	1,331	(3,263)	(5,571)	(10,620)
Provision for write-off of property, plant and equipment	2,131	1,086	3,255	1,916
Non-cash interest expense	150	211	304	634
Compensation and benefits paid or payable in Class A Common Stock	543	195	1,879	1,865
Fair value adjustment on foreign currency option	(10)	2	61	131
Write-off of intangible assets in a discontinued product line		4,149		4,149
Changes in operating assets and liabilities that provided/(used) cash:
Accounts receivable	(4,177)	(4,645)	(48,547)	(19,781)
Contract assets	3,040		(8,721)
Inventories	(2,228)	(3,944)	(12,843)	(17,210)
Prepaid expenses and other current assets	103	(601)	(5,117)	(3,298)
Income taxes prepaid and receivable	(551)		(454)	(2,817)
Accounts payable	(2,728)	(4,769)	6,154	(2,704)
Accrued liabilities	7,565	5,425	12,233	4,525
Income taxes payable	6,766	3,472	13,355	2,964
Noncurrent receivables	(4,676)	(8,107)	(8,846)	(15,643)
Other, net	(5,728)	(4,495)	(9,049)	(557)
Net cash provided by operating activities	44,715	17,898	61,455	21,715
INVESTING ACTIVITIES
Purchases of property, plant and equipment	(21,441)	(15,319)	(60,564)	(61,724)
Purchased software	(78)	(147)	(130)	(538)
Net cash used in investing activities	(21,519)	(15,466)	(60,694)	(62,262)
FINANCING ACTIVITIES
Proceeds from borrowings	3,000	13,076	26,031	45,335
Principal payments on debt	(10,471)	(3,569)	(24,614)	(24,711)
Taxes paid in lieu of share issuance			(1,652)	(1,364)
Proceeds from options exercised	52	356	202	531
Dividends paid	(5,485)	(5,470)	(16,441)	(16,396)
Net cash (used in)/provided by financing activities	(12,904)	4,393	(16,474)	3,395
Effect of exchange rate changes on cash and cash equivalents	(4,443)	7,848	(7,421)	8,875
(Decrease)/increase in cash and cash equivalents	5,849	14,673	(23,134)	(28,277)
Cash and cash equivalents at beginning of period	154,744	138,792	183,727	181,742
Cash and cash equivalents at end of period	$ 160,593	$ 153,465	$ 160,593	$ 153,465