CONSOLIDATED STATEMENTS OF CASH FLOW (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
OPERATING ACTIVITIES
Net income	$ 30,306	$ 1,233	$ 40,788	$ 12,207
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	17,114	15,201	35,416	29,845
Amortization	2,559	2,632	5,205	5,281
Change in other noncurrent liabilities	(854)	(758)	(1,231)	(2,354)
Change in deferred taxes and other liabilities	(6,118)	(6,745)	(6,902)	(7,357)
Provision for write-off of property, plant and equipment	853	534	1,124	830
Non-cash interest expense	154	212	154	423
Compensation and benefits paid or payable in Class A Common Stock	1,047	681	1,336	1,670
Fair value adjustment on foreign currency option	34	75	71	129
Changes in operating assets and liabilities that (used)/provided cash:
Accounts receivable	(12,903)	(14,395)	(44,370)	(15,136)
Contract assets	(13,877)		(11,761)
Inventories	(1,371)	1,655	(10,615)	(13,266)
Prepaid expenses and other current assets	(1,157)	(780)	(5,220)	(2,697)
Income taxes prepaid and receivable	(5)	(2,817)	97	(2,817)
Accounts payable	11,420	(1,459)	8,882	2,065
Accrued liabilities	5,853	10,071	4,668	(900)
Income taxes payable	10,020	1,978	6,589	(508)
Noncurrent receivables	(1,643)	(3,621)	(4,170)	(7,536)
Other, net	(5,745)	4,692	(3,321)	3,938
Net cash provided by operating activities	35,687	8,389	16,740	3,817
INVESTING ACTIVITIES
Purchases of property, plant and equipment	(23,352)	(21,360)	(39,123)	(46,405)
Purchased software	(23)	(353)	(52)	(391)
Net cash used in investing activities	(23,375)	(21,713)	(39,175)	(46,796)
FINANCING ACTIVITIES
Proceeds from borrowings	10,020	16,114	23,031	32,259
Principal payments on debt	(5,653)	(540)	(14,143)	(21,142)
Taxes paid in lieu of share issuance			(1,652)	(1,364)
Proceeds from options exercised	3	100	150	175
Dividends paid	(5,482)	(5,467)	(10,956)	(10,926)
Net cash (used in)/provided by financing activities	(1,112)	10,207	(3,570)	(998)
Effect of exchange rate changes on cash and cash equivalents	(7,882)	(1,424)	(2,978)	1,027
(Decrease)/increase in cash and cash equivalents	3,318	(4,541)	(28,983)	(42,950)
Cash and cash equivalents at beginning of period	151,426	143,333	183,727	181,742
Cash and cash equivalents at end of period	$ 154,744	$ 138,792	$ 154,744	$ 138,792