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		9 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Pension Plan [Member]
Components of net periodic benefit cost
Service cost	$ 97	$ 100	$ 291	$ 300
Interest cost	1,415	1,452	4,245	4,356
Expected return on plan assets	(1,823)	(1,705)	(5,469)	(5,115)
Amortization of net loss(1)	303	336	909	1,008
Net periodic benefit (credit) cost	(8)	183	(24)	549
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	234	897	184
Interest cost	235	202	705	607
Expected return on plan assets	0	0	0	0
Amortization of net loss(1)	(125)	(220)	(375)	(661)
Amortization of unrecognized transition (asset) obligation	0	0	0	0
Amortization of prior service cost (credit)	(439)	(440)	(1,317)	(1,319)
Net periodic benefit (credit) cost	$ (30)	$ (224)	$ (90)	$ (1,189)
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%