Employee Benefit Plans - Components of Net Periodic Benefit Cost and Amounts Recognized in Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
Pension Plan [Member]
Components of net periodic benefit cost
Service cost	$ 97	$ 100	$ 194	$ 200
Interest cost	1,415	1,452	2,830	2,904
Expected return on plan assets	(1,823)	(1,705)	(3,646)	(3,410)
Amortization of net loss(1)	303	336	606	672
Net periodic benefit (credit) cost	(8)	183	(16)	366
Weighted average assumptions used to determine benefit obligations
Discount rate	4.15%	4.50%
Expected long-term return on plan assets	7.50%	8.00%
Other Postretirement Benefit Plan, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	299	(25)	598	(50)
Interest cost	235	163	470	405
Expected return on plan assets	0	0	0	0
Amortization of net loss(1)	(125)	(445)	(250)	(441)
Amortization of unrecognized transition (asset) obligation	0	0	0	0
Amortization of prior service cost (credit)	(439)	(440)	(878)	(879)
Net periodic benefit (credit) cost	$ (30)	$ (747)	$ (60)	$ (965)
Retiree Medical Plan
Weighted average assumptions used to determine benefit obligations
Discount rate			4.29%	4.80%
Death Benefit Plan
Weighted average assumptions used to determine benefit obligations
Discount rate			4.48%	4.53%