Note 10 - Postretirement Medical Benefits - Net Periodic Benefit Cost (Details) - Postretirement Medical Benefits [Member] - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Service cost	$ 159,000	$ 185,000	$ 478,000	$ 554,000
Interest cost	171,000	162,000	512,000	487,000
Recognized prior service cost	12,000	13,000	37,000	38,000
Recognized net actuarial loss	0	10,000	0	31,000
Net periodic benefit cost	$ 342,000	$ 370,000	$ 1,027,000	$ 1,110,000