CONSOLIDATED STATEMENTS OF CASH FLOW (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
OPERATING ACTIVITIES
Net income	$ 10,482	$ 10,974
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation	18,302	14,644
Amortization	2,646	2,649
Change in other noncurrent liabilities	(377)	(1,596)
Change in deferred taxes and other liabilities	(784)	(612)
Provision for write-off of property, plant and equipment	271	296
Non-cash interest expense		211
Compensation and benefits paid or payable in Class A Common Stock	289	989
Fair value adjustment on foreign currency option	37	54
Changes in operating assets and liabilities that (used)/provided cash:
Accounts receivable	(31,467)	(741)
Contract assets	2,116
Inventories	(9,244)	(14,921)
Prepaid expenses and other current assets	(4,063)	(1,917)
Income taxes prepaid and receivable	102
Accounts payable	(2,538)	3,524
Accrued liabilities	(1,185)	(10,971)
Income taxes payable	(3,431)	(2,486)
Noncurrent receivables	2,527	(3,915)
Other, net	(2,630)	(754)
Net cash used in operating activities	(18,947)	(4,572)
INVESTING ACTIVITIES
Purchases of property, plant and equipment	(15,771)	(25,045)
Purchased software	(29)	(38)
Net cash used in investing activities	(15,800)	(25,083)
FINANCING ACTIVITIES
Proceeds from borrowings	13,011	16,145
Principal payments on debt	(8,490)	(20,602)
Taxes paid in lieu of share issuance	(1,652)	(1,364)
Proceeds from options exercised	147	75
Dividends paid	(5,474)	(5,459)
Net cash used in financing activities	(2,458)	(11,205)
Effect of exchange rate changes on cash and cash equivalents	4,904	2,451
Decrease in cash and cash equivalents	(32,301)	(38,409)
Cash and cash equivalents at beginning of period	183,727	181,742
Cash and cash equivalents at end of period	$ 151,426	$ 143,333