Note 9 - Accumulated Other Comprehensive Income/(Loss) - Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Actuarial losses	$ (181)	$ (286)	$ (445)	$ (687)
Prior service (credit) costs	16,007	18,120	32,862	33,511
Total before tax	49,600	34,298	79,635	61,225
Tax benefit	8,748	9,174	14,534	14,986
Amounts reclassified from accumulated other comprehensive loss	40,419	25,030	64,477	44,895
Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Amounts reclassified from accumulated other comprehensive loss	(206)	(243)	(501)	(487)
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	(276)	(347)	(680)	(693)
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Prior service (credit) costs	1	(13)	2	(26)
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	(275)	(360)	(678)	(719)
Tax benefit	69	117	177	232
Amounts reclassified from accumulated other comprehensive loss	$ (206)	$ (243)	$ (501)	$ (487)