Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities:
Net income	$ 59,690	$ 48,866	$ 41,899
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	41,114	44,246	50,638
Deferred income taxes	849	(7,743)	6,699
Non-cash stock based compensation	8,829	6,253	9,047
Change in defined benefit pension plans	(748)	(570)	82
Loss on sale of property and equipment	683	462	2,602
Operating lease expense	7,157	6,173
Gain on sale of patents	(1,978)
Impairment loss		21,206	11,476
Net loss on divestitures		1,587
Other		1,612
Changes in assets and liabilities:
Accounts receivable, net	(46,742)	7,154	3,023
Inventory	(814)	(3,859)	(7,689)
Other assets	(18,240)	7,996	(4,428)
Accounts payable	29,960	(10,253)	12,380
Other liabilities	30,935	(4,327)	(7,295)
Net cash provided by operating activities	110,695	118,803	118,434
Investing Activities:
Purchases of property and equipment	(17,219)	(23,729)	(41,541)
Acquisition of intangible assets	(3,141)
Proceeds from the sale of patents and property and equipment	2,140	219	799
Proceeds from divestiture of businesses, net		44,173
Acquisition of subsidiary, net of cash acquired		(14,823)	(15)
Net cash (used in) provided by investing activities	(18,220)	5,840	(40,757)
Financing Activities:
Borrowing of debt	201,194	37,812	94,679
Repayments of debt	(91,439)	(96,999)	(99,460)
Cash paid for the repurchase of Common Stock	(9,092)	(63,283)	(148,074)
Proceeds from the exercise of Common Stock options	16,552	16,557	14,777
Cash paid for the cancellation of restricted stock	(1,117)	(1,402)	(1,188)
Acquisition contingent consideration payment	(618)
Cash paid for financing costs		(1,278)
Net cash provided by (used in) financing activities	115,480	(108,593)	(139,266)
Foreign currency effect	7,442	(2,722)	(1,963)
Net increase (decrease) in cash, cash equivalents and restricted cash	215,397	13,328	(63,552)
Cash, cash equivalents and restricted cash at beginning of period	52,948	39,620	103,172
Cash, cash equivalents and restricted cash at end of period	268,345	52,948	39,620
Supplemental disclosure of cash flow information:
Cash paid for taxes	5,013	11,008	23,159
Cash paid for interest	$ 4,204	$ 4,462	$ 5,027