Employee Benefit Plans - Other Changes in Plan Assets and Benefit Obligations Recognized in OCI (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2018	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018
Change In Benefit Obligation [Roll Forward]
Projected benefit obligation	$ 144,939	$ 138,412	$ 126,227	$ 144,939
Interest cost		4,236	5,222
Unrecognized actuarial loss		(13,994)	(7,260)
Defined Benefit Plan, Benefit Obligation, Benefits Paid		6,045	6,746
Change in plan assets
Fair value of plan assets at measurement date	104,559	79,819	79,189	104,559
Employer contributions		3,054	3,325
Defined Benefit Plan, Plan Assets, Benefits Paid		6,045	6,746
Projected benefit obligation	144,939	138,412	126,227	144,939
Defined Benefit Plan, Funded (Unfunded) Status of Plan		(58,593)	(47,038)
Amounts recognized in consolidated balance sheets
Cumulative preferred dividends, undeclared and unpaid (1)		1,477	305
Liability, Defined Benefit Plan, Noncurrent		58,593	47,038
Amounts Recognized in Balance Sheet		(58,593)	(47,038)
Other changes recognized in OCI
Total AOCI		76,029	63,652
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, after Tax		(14,779)	(9,193)
Prior service cost (credit)		0	0
Amortization of net loss		(1,479)	(1,506)
Total recognized in OCI		13,300	(2,441)
Net periodic benefit cost		1,309	12,424
Total recognized in net periodic benefit cost and OCI		14,609	9,983
Retiree Medical Plan
Other changes recognized in OCI
Net (gain) loss subject to amortization		0	7,039
Death Benefit Plan
Other changes recognized in OCI
Net (gain) loss subject to amortization		(2,903)	(1,878)
Other Postretirement Benefits Plan
Change In Benefit Obligation [Roll Forward]
Projected benefit obligation	21,283	10,739	24,092	21,283
Service cost	609	446	530
Interest cost	835	725	887
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant		593	605
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment		(13,441)	0
Unrecognized actuarial loss		621	(2,010)
Defined Benefit Plan, Benefit Obligation, Benefits Paid		1,055	1,223
Change in plan assets
Fair value of plan assets at measurement date	0	0	0	0
Employer contributions			462	618
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant			593	605
Defined Benefit Plan, Plan Assets, Benefits Paid			1,055	1,223
Projected benefit obligation	21,283	10,739	24,092	$ 21,283
Defined Benefit Plan, Funded (Unfunded) Status of Plan		(10,739)	(24,092)
Amounts recognized in consolidated balance sheets
Cumulative preferred dividends, undeclared and unpaid (1)		744	1,068
Liability, Defined Benefit Plan, Noncurrent		9,995	23,024
Amounts Recognized in Balance Sheet		(10,739)	(24,092)
Other changes recognized in OCI
Net (gain) loss subject to amortization		(2,714)	(5,160)
Transition obligation recognized in AOCI		(8,961)	(6,936)
Total AOCI		(11,675)	(12,096)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, after Tax		621	(2,010)
Prior service cost (credit)		(13,441)	0
Amortization of net loss		3,068	835
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, after Tax		(11,416)	(1,757)
Total recognized in OCI		422	4,602
Net periodic benefit cost	$ (1,154)	(13,312)	(1,174)
Total recognized in net periodic benefit cost and OCI		$ (12,890)	$ 3,428