Employee Benefit Plans - Components of Net Periodic Benefit Cost and Amounts Recognized in Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Components of net periodic benefit cost
Pension settlement charge	$ 0	$ 0	$ 10,948	$ 0
Pension Plan
Components of net periodic benefit cost
Service cost	0	0	0	0
Interest cost	1,173	1,432	4,025	4,296
Expected return on plan assets	(1,126)	(1,456)	(4,096)	(4,368)
Amortization of net loss (gain)	380	418	1,120	1,254
Pension settlement charge	0	0	10,948	0
Net periodic benefit (credit) cost	427	394	$ 11,997	$ 1,182
Weighted average assumptions used to determine benefit obligations
Discount rate			4.10%	3.80%
Expected long-term return on plan assets			6.75%	6.75%
Other Postretirement Benefit Plan
Components of net periodic benefit cost
Service cost	133	152	$ 399,000	$ 456,000
Interest cost	222	209	666,000	627,000
Amortization of net loss (gain)	(209)	(210)	(627,000)	(630,000)
Net periodic benefit (credit) cost	$ (293)	$ (288)	$ (879,000)	$ (864,000)
Retiree Medical Plan
Weighted average assumptions used to determine benefit obligations
Discount rate			4.25%	4.13%
Death Benefit Plan
Weighted average assumptions used to determine benefit obligations
Discount rate			4.25%	4.12%