CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities
Net income	$ 99,229	$ 154,115	$ 105,406
Adjustments to reconcile net income to net cash provided by operating activities, net of effects of acquisitions:
Depreciation	91,747	91,543	86,291
Amortization of intangible assets	16,260	18,041	18,353
Amortization of debt issuance costs	1,455	521	522
Share-based compensation	25,260	20,535	20,736
Loss (gain) on disposal of property, plant and equipment	119	(24,429)	(636)
Deferred income taxes	(14,456)	9,904	3,674
Other	(949)	(187)	(2,335)
Changes in operating assets:
Accounts receivable	(10,501)	(30,775)	(29,478)
Inventories	(4,560)	(11,325)	(2,154)
Prepaid expenses and other current assets	(9,067)	(6,630)	(11,119)
Changes in operating liabilities:
Accounts payable	7,422	3,513	9,977
Accrued liabilities	(9,198)	7,369	(13,445)
Other liabilities	(2,182)	(2,694)	345
Income taxes payable (refundable)	(3,359)	271	(571)
Net cash and cash equivalents provided by operating activities	187,220	229,772	185,566
Investing Activities
Acquisitions, net of cash acquired	(24,593)	(33,028)	(41)
Purchases of short-term investments	(11,486)	(19,271)	(15,901)
Sales of short-term investments	10,277	21,847	12,576
Purchase of equity securities	(6,131)
Purchases of property, plant and equipment	(75,813)	(98,505)	(87,507)
Proceeds from sales of property, plant and equipment	232	29,366	429
Other	742	(835)	1,500
Net cash and cash equivalents used by investing activities	(106,772)	(100,426)	(88,944)
Financing Activities
Advances on lines of credit and short-term debt	77,483	9,954	9,151
Repayments on lines of credit and short-term debt	(40,498)	(7,362)	(2,797)
Proceeds from long-term debt	956,363	405,540	465,656
Repayments of long-term debt	(744,237)	(522,860)	(522,473)
Debt issuance costs	(2,477)	(223)
Repayments of finance lease obligations	(919)	(1,082)	1,198
Net proceeds from the issuance of common stock	6,830	11,901	4,862
Capital contribution from noncontrolling interest	10		6,255
Dividend distribution to noncontrolling interest	(2,112)	(3,818)	(2,694)
Repurchase of common stock	(296,705)
Taxes related to net share settlement	(8,302)	(4,432)	(11,294)
Other	262	(50)	225
Net cash and cash equivalents used by financing activities	(54,302)	(112,432)	(51,911)
Effect of exchange rate changes on cash and cash equivalents, including restricted cash	34,876	760	(8,078)
Increase (decrease) in cash and cash equivalents, including restricted cash	61,022	17,674	36,633
Cash and cash equivalents, beginning of year, including restricted cash	259,507	241,833	205,200
Cash and cash equivalents, end of year, including restricted cash	320,529	259,507	241,833
Cash paid during the year for:
Interest	10,219	7,235	9,962
Income taxes	48,040	37,158	33,265
Non-cash activities:
Accounts payable balance related to the purchase of property, plant and equipment	$ 7,297	$ 10,167	$ 12,598