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
	Sep. 30, 2013		Sep. 30, 2012
Retiree Medical Plan
Weighted average assumptions used to determine benefit obligations
Discount rate	4.20%		4.20%
Postretirement Benefits Other Than Pension
Components of net periodic benefit cost
Service cost	$ 493		$ 493
Interest cost	242		242
Expected return on plan assets	0		0
Amortization of net (gain) loss	4		4
Amortization of unrecognized transition (asset) obligation	0		0
Amortization of prior service cost (credit)	(439)		(439)
Net periodic benefit cost	300		300
Pension Plan
Components of net periodic benefit cost
Service cost	100		119
Interest cost	1,452		1,449
Expected return on plan assets	(1,705)		(1,660)
Amortization of net (gain) loss	336	[1]	387	[1]
Amortization of prior service cost (credit)	0		5
Net periodic benefit cost	$ 183		$ 300
Weighted average assumptions used to determine benefit obligations
Discount rate	4.50%		4.55%
Expected long-term return on plan assets	8.00%		8.00%
Death Benefit Plan
Weighted average assumptions used to determine benefit obligations
Discount rate	4.39%		4.39%

[1] These amounts represent the estimated portion of the net (gain) loss and net prior service cost (credit) remaining in AOCI that is expected to be recognized as a component of net periodic benefit cost over the current fiscal year.