Note 12 - Employee Benefit and Retirement Plans - Status of the Postretirement Medical and Life Insurance Benefit Plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2017	Dec. 31, 2016
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate				4.31%	3.77%
Fair value of plan assets at beginning of year	$ 118,693
Fair value of plan assets at end of year	122,033	$ 118,693
U.S. Post Retirement Medical and Life Insurance Plan [Member]
Benefit obligation at beginning of year	6,385	7,086	$ 7,381
Service cost	72	85	85
Interest cost	265	270	269
Benefits paid	(346)	(388)	(483)
Actuarial (gain) loss	554	(668)	(166)
Benefit obligation at end of year	$ 6,930	$ 6,385	$ 7,086
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.56%	4.27%	3.92%
Rate of compensation increase	2.64%	2.64%	2.64%
Fair value of plan assets at beginning of year
Employer contributions	346	388	483
Benefits paid	(346)	(388)	(483)
Fair value of plan assets at end of year
Current liability	(353)	(339)	(370)
Noncurrent liability	(6,577)	(6,046)	(6,716)
Net amount recognized in balance sheet	$ (6,930)	$ (6,385)	$ (7,086)
Discount rate	4.27%	3.92%	3.77%
Rate of compensation increase	2.64%	2.64%	2.64%
Prior service cost	$ 2,777	$ 3,314	$ 3,851
Accumulated loss	(1,452)	(928)	(1,696)
Amounts not yet recognized as a component of net periodic benefit cost	1,325	2,386	2,155
Accumulated net periodic benefit cost in excess of contributions	(8,255)	(8,771)	(9,241)
Prior service cost	(537)	(537)	(673)
Amortization of accumulated loss	30	99	121
Net periodic benefit cost	(170)	(83)	(198)
Prior service cost	537	537	537
Net loss	(83)	(30)	(99)
	$ 454	$ 507	$ 438
Healthcare cost trend rate assumed for next year	6.30%	6.60%	6.60%
Rate to which the cost trend rate gradually declines	4.50%	4.50%	4.50%
Year that the rate reaches the rate at which it is assumed to remain	2037	2037	2037