Note 5 - Accumulated Other Comprehensive Loss - Disclosure of Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Beginning Balance	$ 554,320
Other comprehensive income (loss)	(2,615)	$ 18,965	$ (17,688)
Ending Balance	761,261	554,320
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Beginning Balance	(12,856)	(28,047)
Other comprehensive income (loss) before reclassifications	(5,976)	15,191
Amounts reclassified from AOCL
Other comprehensive income (loss)	(5,976)	15,191
Ending Balance	(18,832)	(12,856)	(28,047)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Beginning Balance	(10,978)	(11,040)
Other comprehensive income (loss) before reclassifications	(156)	(591)
Amounts reclassified from AOCL	593	653
Other comprehensive income (loss)	437	62
Ending Balance	(10,541)	(10,978)	(11,040)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Beginning Balance	2,636	(1,076)
Other comprehensive income (loss) before reclassifications	2,924	3,712
Other comprehensive income (loss)	2,924	3,712
Ending Balance	5,560	2,636	(1,076)
AOCI Attributable to Parent [Member]
Beginning Balance	(21,198)	(40,163)	(22,475)
Other comprehensive income (loss) before reclassifications	(3,208)	18,312
Amounts reclassified from AOCL	593	653
Other comprehensive income (loss)	(2,615)	18,965
Ending Balance	$ (23,813)	$ (21,198)	$ (40,163)