Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Activities
Net income	$ 32,585	$ 52,812	$ 57,265
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	61,517	58,106	52,974
Amortization	10,439	9,355	7,140
Change in other noncurrent liabilities	(10,145)	(5,232)	3,608
Change in deferred taxes and other liabilities	(1,264)	5,889	(29,517)
Provision for write-off of property, plant and equipment	2,870	2,778	867
Fair value adjustment on available-for-sale assets			3,212
Gain on disposition or involuntary conversion of assets			(1,056)
Non-cash interest expense	660	564
Write-off of pension liability adjustment due to settlement		51	103
Compensation and benefits paid or payable in Class A Common Stock	2,133	2,433	1,707
Write-off of intangible assets in a discontinued product line	4,149
Changes in operating assets and liabilities that provide/(use) cash, net of impact of business acquisition:
Accounts receivable	(21,859)	(12,697)	(404)
Inventories	3,090	(12,520)	(8,277)
Prepaid expenses and other current assets	(4,989)	(2,595)	1,253
Income taxes prepaid and receivable	(941)	(2,206)	(3,156)
Contract receivable	(18,766)	(14,045)
Accounts payable	2,910	2,108	(6,001)
Accrued liabilities	5,303	1,312	2,081
Income taxes payable	(799)	1,398	9,072
Other, net	(2,677)	(6,571)	7,139
Net cash provided by operating activities	64,216	80,940	98,010
Investing Activities
Purchase of business, net of cash acquired		(187,000)
Purchases of property, plant and equipment	(85,510)	(71,244)	(48,622)
Purchased software	(2,127)	(2,248)	(1,973)
Proceeds from sale or involuntary conversion of assets		6,939	2,797
Net cash used in investing activities	(87,637)	(253,553)	(47,798)
Financing Activities
Proceeds from borrowings	115,334	235,907	95,126
Principal payments on debt	(84,047)	(34,356)	(102,215)
Debt acquisition costs	(2,130)	(1,771)	(1,673)
Cash received/(paid) to settle swap agreements	6,346	(5,175)
Proceeds from options exercised	597	517	1,897
Taxes paid in lieu of share issuance	(1,364)	(1,272)	(1,449)
Dividends paid	(21,869)	(21,812)	(21,088)
Net cash provided by/(used in) financing activities	12,867	172,038	(29,402)
Effect of exchange rate changes on cash and cash equivalents	12,539	(2,796)	(15,499)
Increase/(decrease) in cash and cash equivalents	1,985	(3,371)	5,311
Cash and cash equivalents at beginning of year	181,742	185,113	179,802
Cash and cash equivalents at end of year	$ 183,727	$ 181,742	$ 185,113