Note 9 - Accumulated Other Comprehensive Income/(Loss) - Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Actuarial losses	$ (264)	$ (401)
Prior service costs	16,855	15,391
Total before tax	30,035	26,927
Provision for income taxes	5,786	5,812
Amounts reclassified from accumulated other comprehensive loss	24,058	19,865
Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Amounts reclassified from accumulated other comprehensive loss	(295)	(244)
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Actuarial losses	(404)	(346)
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Prior service costs	1	(13)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Total before tax	(403)	(359)
Provision for income taxes	108	115
Amounts reclassified from accumulated other comprehensive loss	$ (295)	$ (244)