Note 13 - Guarantor Subsidiaries - Unaudited Interim Condensed Consolidating Statements of Cash Flows (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities	$ 74,115	$ 173,114
Additions to properties, plants, and equipment	(70,390)	(120,236)
Other investing activities, net	1,156	(29,159)
Dividends paid to shareholders	(3,392)	(3,296)
Proceeds from (payments on) debt	(5,535)	(8,135)
Other financing activity, net	6,141	3,651
Effect of exchange rates on cash	1,051	627
Changes in cash and cash equivalents	3,146	12,635
Cash and cash equivalents at beginning of period	169,777	155,209
Cash and cash equivalents at end of period	172,923	167,844
Acquisitions of other companies, net of cash acquired		(3,931)
Consolidation, Eliminations [Member]
Cash flows from operating activities	(24,155)	45,280
Additions to properties, plants, and equipment
Other investing activities, net	(5,339)
Dividends paid to shareholders
Proceeds from (payments on) debt
Other financing activity, net	29,494	(45,280)
Effect of exchange rates on cash
Changes in cash and cash equivalents
Cash and cash equivalents at beginning of period
Cash and cash equivalents at end of period
Acquisitions of other companies, net of cash acquired
Parent Company [Member] | Reportable Legal Entities [Member]
Cash flows from operating activities	35,764	14,525
Additions to properties, plants, and equipment		(348)
Other investing activities, net	176	(24,696)
Dividends paid to shareholders	(3,392)	(3,296)
Proceeds from (payments on) debt
Other financing activity, net	(44,762)	33,335
Effect of exchange rates on cash
Changes in cash and cash equivalents	(12,214)	15,589
Cash and cash equivalents at beginning of period	113,275	94,167
Cash and cash equivalents at end of period	101,061	109,756
Acquisitions of other companies, net of cash acquired		(3,931)
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Cash flows from operating activities	41,071	51,599
Additions to properties, plants, and equipment	(28,220)	(71,265)
Other investing activities, net	6,903	(816)
Dividends paid to shareholders
Proceeds from (payments on) debt	(4,518)	(7,477)
Other financing activity, net	(21,500)	24,522
Effect of exchange rates on cash
Changes in cash and cash equivalents	(6,264)	(3,437)
Cash and cash equivalents at beginning of period	24,388	42,692
Cash and cash equivalents at end of period	18,124	39,255
Acquisitions of other companies, net of cash acquired
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Cash flows from operating activities	21,435	61,710
Additions to properties, plants, and equipment	(42,170)	(48,623)
Other investing activities, net	(584)	(3,647)
Dividends paid to shareholders
Proceeds from (payments on) debt	(1,017)	(658)
Other financing activity, net	42,909	(8,926)
Effect of exchange rates on cash	1,051	627
Changes in cash and cash equivalents	21,624	483
Cash and cash equivalents at beginning of period	32,114	18,350
Cash and cash equivalents at end of period	$ 53,738	18,833
Acquisitions of other companies, net of cash acquired