Employee Benefit Plans - Amortization Schedule (Details) - USD ($) $ in Thousands	12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Retiree Medical Plan
Amortization of Net (Gain) Loss Calculation
Net (gain) loss	$ 0	$ (7,039)
Net (gain) loss subject to amortization	0	(7,039)
Corridor (10% of greater of APBO or assets)	0	1,490
Net (gain)/loss in excess of corridor	0	$ (5,549)
Amortization years		8 years 7 months 6 days
Death Benefit Plan
Amortization of Net (Gain) Loss Calculation
Net (gain) loss	2,903	$ 1,878
Net (gain) loss subject to amortization	2,903	1,878
Corridor (10% of greater of APBO or assets)	1,043	919
Net (gain)/loss in excess of corridor	$ 1,860	$ 959
Amortization years	5 years 9 months 18 days	6 years 6 months