Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Income	$ 86,870	$ 101,035	$ 28,793
Depreciation and amortization	85,631	76,916	74,735
Operatingleaserightofuseassetamortization	9,216	8,294	0
Provision for doubtful accounts	7,137	14,882	781
Provision for warranty and returns	(1,576)	(134)	5,353
Stock compensation	23,954	21,918	24,241
Gain (Loss) on Disposition of Property Plant Equipment	(1,789)	12,872	8,867
Contractsettlement	0	0	12,696
Impairment of Intangible Assets, Finite-lived	0	0	5,000
Bond premium amortization	231	135	342
Debt issuance cost amortization	288	288	288
Impairment of assets held for sale	0	0	269
Change in fair value of contingent earn-out	9,000	(47,400)	20,400
Production Related Impairments or Charges	2,626	0	0
Sparepartsusage	11,191	24,301	7,310
Other	6,939	447	3,856
Increase (Decrease) in Accounts Receivable	78,049	(23,684)	(76,742)
Increase (Decrease) in Inventories	19,196	(24,997)	(21,770)
Increase (Decrease) in Prepaid Expense and Other Assets	(4,311)	8,588	3,719
Increase (Decrease) in Due from Related Parties, Current	0	0	97,443
Increase (Decrease) in Other Operating Assets	(16,069)	(29,837)	(9,086)
Accounts payable	(46,415)	(2,697)	23,270
Accrued liabilities	(29,379)	(43,689)	(29,553)
Income taxes, including excess tax benefits and deferred income taxes	(18,037)	4,680	(19,997)
Net cash provided by operating activities	222,752	101,918	160,215
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(92,005)	(97,312)	(92,720)
Proceeds from Sale of Other Property, Plant, and Equipment	6,176	33	765
Proceeds from Sale of Property Held-for-sale	0	0	13,000
Intangible asset additions	(8,385)	(8,728)	(8,059)
Business acquisitions, net of cash acquired	0	(76,133)	(1,300)
Purchases of investment securities	(32,825)	(26,040)	(30,496)
Proceeds from sale of investment securities	28,900	41,292	15,440
Net cash (used in) provided by investing activities	(98,139)	(166,888)	(103,370)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from Long-term Lines of Credit	150,000	0	0
Repayments of Long-term obligations	(150,000)	0	0
Proceeds from exercise of stock options	13,193	7,732	14,275
Finance Lease, Principal Payments	(357)	0	0
Purchase of treasury stock	(12,876)	(18,639)	(6,252)
Net cash (used in) provided by financing activities	(40)	(10,907)	8,023
Effect of Exchange Rate on Cash [Abstract]
Effect of exchange rate changes on cash	2,854	(234)	(10,159)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect, Total	127,427	(76,111)	54,709
CASH AND CASH EQUIVALENTS, beginning of period	268,670	344,781	290,072
CASH AND CASH EQUIVALENTS, end of period	396,097	268,670	344,781
SUPPLEMENTAL DISCLSOURE OF CASH FLOW INFORMATION
Cash paid during the year for income taxes	31,628	9,675	12,598
Interest Paid, Excluding Capitalized Interest, Operating Activities	1,753	549	709
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING ACTIVITIES
Accounts payable for property and equipment	$ 2,211	13,912	26,522
Fair value of assets acquired		91,019
Cash paid for acquisitions, net of cash acquired		(76,133)
Contingent consideration		(17,300)
Goodwill, Acquired During Period		20,026	$ 1,300
Liabilities Assumed		$ (17,612)