Note 10 - Postretirement Medical Benefits - Net Periodic Benefit Cost (Details) - Postretirement Medical Benefits [Member] - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Service cost	$ 159,000	$ 184,000	$ 318,000	$ 369,000
Interest cost	171,000	163,000	342,000	325,000
Recognized prior service cost	12,000	12,000	25,000	25,000
Recognized net actuarial loss (gain)	0	11,000	0	21,000
Net periodic benefit cost	$ 342,000	$ 370,000	$ 685,000	$ 740,000