Employee Benefit Plans - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2018	Jun. 30, 2020	Jun. 30, 2019
Defined Benefit Plan Disclosure
Interest cost		$ 4,236	$ 5,222
Amortization of net gain		1,479	1,506
Net periodic benefit cost		1,309	12,424
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure
Service cost	$ 609	446	530
Interest cost	835	725	887
Amortization of net gain	(841)	(3,067)	(834)
Curtailment credit - Retiree Medical	0	5,750	0
Amortization of prior service credit	(1,757)	(5,666)	(1,757)
Net periodic benefit cost	$ (1,154)	$ (13,312)	$ (1,174)