Retirement Benefits - Summary of other postretirement benefit plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018
Amounts recognized on the Consolidated Balance Sheet
Pensions and other postretirement benefits	$ (1,887,414)	$ (1,304,379)
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Expense related to other postretirement benefits	1,551	1,838	$ 2,755
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	60,998	66,521
Service cost	250	205
Interest cost	1,686	2,043
Acquisition	12,638	0
Actuarial loss (gain)	1,276	(3,235)
Benefits paid	(4,718)	(4,536)
Benefit obligation at end of year	72,130	60,998	$ 66,521
Funded status	(72,130)	(60,998)
Amounts recognized on the Consolidated Balance Sheet
Other accrued liabilities	(6,374)	(5,308)
Pensions and other postretirement benefits	(65,756)	(55,690)
Net amount recognized	(72,130)	(60,998)
Amounts recognized in Accumulated Other Comprehensive (Loss)
Net actuarial gain	(173)	(1,713)
Prior service credit	(73)	(194)
Net amount recognized	$ (246)	$ (1,907)