Consolidated Condensed Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating Activities:
Net income	$ 12,966	$ 25,402
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	12,892	10,192
Deferred income taxes	(707)	676
Stock compensation	2,202	2,303
Defined benefit plan expense	298	(16)
Provision of doubtful accounts	41	(54)
Loss on sale of property and equipment	85	103
Changes in operating assets and liabilities:
Accounts receivable	(9,691)	(13,900)
Inventory	1,903	(2,407)
Prepaid expenses and other assets	(4,881)	(6,492)
Accounts payable	1,290	1,094
Accrued liabilities	(10,808)	(38,237)
Net cash provided by (used in) operating activities	5,590	(21,336)
Investing Activities:
Final payment for acquisition of subsidiary, net of cash acquired	(15)	(2,000)
Purchases of property and equipment	(8,378)	(13,552)
Net cash used in investing activities	(8,393)	(15,552)
Financing Activities:
Repayments of debt	(35,492)	(8,427)
Cash paid for the cancellation of restricted stock	(659)	(926)
Proceeds from the exercise of Common Stock options	751	881
Net cash used in financing activities	(35,400)	(8,472)
Foreign currency effect	5,513	2,080
Net decrease in cash and cash equivalents	(32,690)	(43,280)
Cash and cash equivalents at beginning of period	103,172	177,187
Cash and cash equivalents at end of period	70,482	133,907
Supplemental disclosure of cash flow information:
Cash paid for taxes	6,870	51,618
Cash paid for interest	981	858
Supplemental disclosure of non-cash transactions:
Common Stock issued to Board of Directors and employees	$ 1,362	$ 1,125