Consolidated Condensed Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating Activities:
Net income	$ 29,625	$ 33,915
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	25,823	21,191
Deferred income taxes	(1,799)	(2,278)
Stock compensation	4,063	4,761
Defined benefit plan expense	(103)	94
Provision of doubtful accounts	204	6
Loss on sale of property and equipment	2,156	249
Changes in operating assets and liabilities:
Accounts receivable	(17,469)	(6,949)
Inventory	1,631	1,149
Prepaid expenses and other assets	(12,094)	(5,147)
Accounts payable	10,540	(2,932)
Accrued liabilities	(10,034)	(37,944)
Net cash provided by operating activities	32,543	6,115
Investing Activities:
Proceeds from the sale of property and equipment	698	34
Final payment for acquisition of subsidiary, net of cash acquired	(15)	(2,000)
Purchases of property and equipment	(22,138)	(25,750)
Net cash used in investing activities	(21,455)	(27,716)
Financing Activities:
Borrowing of debt	15,000
Repayments of debt	(46,742)	(8,428)
Cash paid for the cancellation of restricted stock	(882)	(1,100)
Proceeds from the exercise of Common Stock options	4,966	2,061
Repurchase of Common Stock	(20,241)	(53)
Net cash used in financing activities	(47,899)	(7,520)
Foreign currency effect	(1,004)	16,111
Net decrease in cash and cash equivalents	(37,815)	(13,010)
Cash and cash equivalents at beginning of period	103,172	177,187
Cash and cash equivalents at end of period	65,357	164,177
Supplemental disclosure of cash flow information:
Cash paid for taxes	18,100	58,831
Cash paid for interest	2,608	2,190
Supplemental disclosure of non-cash transactions:
Common Stock issued to Board of Directors and employees	$ 2,419	$ 2,229