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, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Pension Plan
Components of net periodic benefit cost
Service cost	$ 124	$ 97	$ 372	$ 291
Interest cost	1,397	1,546	4,191	4,638
Expected return on plan assets	(1,607)	(1,710)	(4,821)	(5,130)
Amortization of net loss (gain)	508	370	1,524	1,110
Net periodic benefit (credit) cost	422	303	$ 1,266	$ 909
Weighted average assumptions used to determine benefit obligations
Discount rate			3.55%	4.40%
Expected long-term return on plan assets			7.75%	7.50%
Other Postretirement Benefit Plan
Components of net periodic benefit cost
Service cost	190	347	$ 570	$ 1,041
Interest cost	207	299	621	897
Amortization of net loss (gain)	(157)	(49)	(471)	(147)
Amortization of net prior service credit	(439)	(439)	(1,317)	(1,317)
Net periodic benefit (credit) cost	$ (199)	$ 158	$ (597)	$ 474
Retiree Medical Plan
Weighted average assumptions used to determine benefit obligations
Discount rate			3.73%	4.69%
Death Benefit Plan
Weighted average assumptions used to determine benefit obligations
Discount rate			3.79%	4.74%