Note 16 - Guarantor Subsidiaries - Unaudited Interim Condensed Consolidating Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities	$ 115,878	$ 225,328	$ 106,445
Additions to properties, plants, and equipment	(98,038)	(164,788)	(137,443)
Other investing activities, net	2,643	(29,946)	(1,163)
Dividends paid to stockholders	(4,528)	(4,419)	(4,291)
Payments on debt	(6,986)	(11,156)	(10,851)
Other financing activity	6,266	3,554	(2,001)
Effect of exchange rate changes on cash	1,095	(74)	(5,152)
Changes in cash and cash equivalents	16,330	14,568	(54,456)
Cash and cash equivalents at beginning of year	169,777	155,209	209,665
Purchase of other companies, net of cash acquired		(3,931)	(809)
Dividends paid to stockholders	(4,528)	(4,419)	(4,291)
Payments on debt	(6,986)	(11,156)	(10,851)
Consolidation, Eliminations [Member]
Cash flows from operating activities	228,797	(19,606)	(2,629)
Additions to properties, plants, and equipment
Other investing activities, net	(138,762)
Dividends paid to stockholders
Payments on debt
Other financing activity	(90,035)	19,606	2,629
Effect of exchange rate changes on cash
Changes in cash and cash equivalents
Cash and cash equivalents at beginning of year
Purchase of other companies, net of cash acquired
Dividends paid to stockholders
Payments on debt
Parent Company [Member] | Reportable Legal Entities [Member]
Cash flows from operating activities	(134,900)	85,665	(56,036)
Additions to properties, plants, and equipment		(348)	(1,355)
Other investing activities, net	132,118	(29,383)	(748)
Dividends paid to stockholders	(4,528)	(4,419)	(4,291)
Payments on debt
Other financing activity	(2,087)	(28,476)	9,712
Effect of exchange rate changes on cash
Changes in cash and cash equivalents	(9,397)	19,108	(52,718)
Cash and cash equivalents at beginning of year	113,275	94,167	146,885
Purchase of other companies, net of cash acquired		(3,931)
Dividends paid to stockholders	(4,528)	(4,419)	(4,291)
Payments on debt
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Cash flows from operating activities	(98,046)	82,778	101,254
Additions to properties, plants, and equipment	(46,570)	(93,541)	(97,684)
Other investing activities, net	9,287	(896)	637
Dividends paid to stockholders
Payments on debt	(5,242)	(10,174)	(12,405)
Other financing activity	147,199	3,529	17,066
Effect of exchange rate changes on cash
Changes in cash and cash equivalents	6,628	(18,304)	8,868
Cash and cash equivalents at beginning of year	24,388	42,692	33,824
Purchase of other companies, net of cash acquired
Dividends paid to stockholders
Payments on debt	(5,242)	(10,174)	(12,405)
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Cash flows from operating activities	120,027	76,491	63,856
Additions to properties, plants, and equipment	(51,468)	(70,899)	(38,404)
Other investing activities, net		333	(1,052)
Dividends paid to stockholders
Payments on debt	(1,744)	(982)	1,554
Other financing activity	(48,811)	8,895	(31,408)
Effect of exchange rate changes on cash	1,095	(74)	(5,152)
Changes in cash and cash equivalents	19,099	13,764	(10,606)
Cash and cash equivalents at beginning of year	32,114	18,350	28,956
Purchase of other companies, net of cash acquired
Dividends paid to stockholders
Payments on debt	$ (1,744)	$ (982)	$ 1,554