Note 9 - Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	$ 544,864
Ending balance	592,737
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(12,040)	$ (34,290)
Other comprehensive income before reclassifications	2,929	2,468
Net current-period other comprehensive income	2,929	2,468
Ending balance	(9,111)	(31,822)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(30,188)	(31,230)
Amounts reclassified from accumulated other comprehensive loss	295	244
Net current-period other comprehensive income	295	244
Ending balance	(29,893)	(30,986)
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(42,228)	(65,520)
Other comprehensive income before reclassifications	2,929	2,468
Amounts reclassified from accumulated other comprehensive loss	295	244
Net current-period other comprehensive income	3,224	2,712
Ending balance	$ (39,004)	$ (62,808)