Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities:
Net income	$ 59,415,000	$ 135,601,000	$ 121,380,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	90,150,000	80,154,000	78,242,000
Gain on disposition of property, plant and equipment	(246,000)	(349,000)	(1,128,000)
Stock compensation expense	12,279,000	11,493,000	9,258,000
Pension lump-sum settlement charge	0	0	9,856,000
Effect of U.S. Tax Reform on deferred tax assets	4,152,000	0	0
Changes in assets and liabilities, net of the effects of acquisitions:
Accounts receivable	(50,082,000)	(23,057,000)	14,027,000
Inventories	(173,000)	1,989,000	(1,190,000)
Prepaid expenses and other current assets	(4,241,000)	569,000	(2,645,000)
Accounts payable	12,018,000	11,778,000	(2,936,000)
Accrued liabilities	14,439,000	15,825,000	(14,166,000)
Deferred income taxes	3,589,000	(2,210,000)	3,121,000
Long-term retirement benefits	(16,349,000)	(15,492,000)	1,081,000
Long-term tax liability	79,770,000	0	0
Other	(801,000)	1,345,000	2,575,000
Net cash provided by operating activities	203,920,000	217,646,000	217,475,000
Investing activities:
Proceeds from disposition of property, plant and equipment	2,594,000	780,000	3,442,000
Capital expenditures	(58,712,000)	(47,577,000)	(45,982,000)
Business acquisitions, net of cash acquired	(8,922,000)	(128,613,000)	(51,954,000)
Component Repair Program payments	0	(4,100,000)	(21,000,000)
Other	(3,000,000)	0	0
Net cash used in investing activities	(68,040,000)	(179,510,000)	(115,494,000)
Financing activities:
Net change in other borrowings	(25,304,000)	8,375,000	14,680,000
Payments on long-term debt	(73,161,000)	(321,506,000)	(171,198,000)
Proceeds from the issuance of long-term debt	129,118,000	303,277,000	159,264,000
Proceeds from the issuance of common stock	2,408,000	4,611,000	11,425,000
Common stock repurchases	(40,791,000)	(20,520,000)	(52,103,000)
Dividends paid	(29,551,000)	(27,435,000)	(26,176,000)
Withholding taxes paid on stock issuances	(5,380,000)	(4,885,000)	(4,913,000)
Other	(21,090,000)	4,771,000	9,850,000
Net cash used by financing activities	(63,751,000)	(53,312,000)	(59,171,000)
Effect of exchange rate changes on cash flows	6,714,000	(2,303,000)	(4,923,000)
Increase (decrease) in cash and cash equivalents	78,843,000	(17,479,000)	37,887,000
Cash and cash equivalents at beginning of year	66,447,000	83,926,000	46,039,000
Cash and cash equivalents at end of year	$ 145,290,000	$ 66,447,000	83,926,000
Supplemental Disclosure of Cash Flow Information:
Intangible assets acquired			$ 3,200,000