Employee Benefit Plans - Components of Net Periodic Benefit Cost and Amounts Recognized in Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Pension Plan [Member]
Components of net periodic benefit cost
Service cost	$ 124	$ 97
Interest cost	1,397	1,546
Expected return on plan assets	(1,607)	(1,710)
Amortization of net loss (gain)	508	370
Net periodic benefit (credit) cost	$ 422	$ 303
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 [Member]
Components of net periodic benefit cost
Service cost	$ 190	$ 347
Interest cost	207	299
Amortization of net loss (gain)	(157)	(49)
Amortization of net prior service credit	(439)	(439)
Net periodic benefit (credit) cost	$ (199)	$ 158
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%