Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Activities:
Net Income	$ 41,899	$ 35,227	$ 76,598
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	50,638	44,972	37,764
Deferred income taxes	6,699	5,135	(8,843)
Stock compensation	9,047	12,507	9,186
Defined benefit pension plan (income) expense	82	(23)	184
Provision for doubtful accounts	(1)	(469)	108
Loss on sale of property and equipment	2,602	1,042	468
Impairment loss	11,476
Changes in operating assets and liabilities:
Accounts receivable	3,024	6,033	(17,971)
Inventory	(7,689)	(4,348)	(5,933)
Prepaid expenses and other assets	(4,428)	(12,334)	9,106
Accounts payable	12,380	(7,691)	4,419
Accrued liabilities	(7,295)	(30,171)	3,314
Net cash provided by operating activities	118,434	49,880	108,400
Investing Activities:
Investment in subsidiary, net of cash acquired	(15)	(66,994)	(73,593)
Investment in development-stage entity			(4,486)
Purchases of property and equipment	(41,541)	(50,785)	(66,316)
Proceeds from the sale of property and equipment	799	91	57
Net cash used in investing activities	(40,757)	(117,688)	(144,338)
Financing Activities:
Cash paid for financing costs			(649)
Borrowing of Debt	94,679		115,000
Repayments of Debt	(99,460)	(27,156)	(42,244)
Cash paid for the cancellation of restricted stock	(1,188)	(1,837)	(1,196)
Cash paid for the repurchase of common stock	(148,074)	(5,326)
Excess tax benefit from equity awards			7,509
Proceeds from the exercise of Common Stock options	14,777	2,755	1,438
Net cash (used in) provided by financing activities	(139,266)	(31,564)	79,858
Foreign currency effect on cash and cash equivalents	(1,963)	25,357	(11,212)
Net (decrease) increase in cash and cash equivalents	(63,552)	(74,015)	32,708
Cash and cash equivalents at beginning of period	103,172	177,187	144,479
Cash and cash equivalents at end of period	39,620	103,172	177,187
Supplemental disclosure of cash flow information:
Cash paid for interest	5,027	4,540	3,029
Cash paid for taxes	23,159	76,741	21,608
Supplemental disclosure of non-cash transactions:
Common Stock issued to directors and employees	$ 5,759	$ 6,298	$ 4,589