Employee Benefit Plans - Components of Net Periodic Benefit Cost and Amounts Recognized in Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Pension Plan [Member]
Components of net periodic benefit cost
Service cost	$ 124	$ 97	$ 248	$ 194
Interest cost	1,397	1,546	2,794	3,092
Expected return on plan assets	(1,607)	(1,710)	(3,214)	(3,420)
Amortization of net loss (gain)	508	370	1,016	740
Net periodic benefit (credit) cost	422	303	$ 844	$ 606
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	$ 380	$ 694
Interest cost	207	299	414	598
Amortization of net loss (gain)	(157)	(49)	(314)	(98)
Amortization of net prior service credit	(439)	(439)	(878)	(878)
Net periodic benefit (credit) cost	$ (199)	$ 158	$ (398)	$ 316
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%