Employee Benefit Plans - Amortization Schedule (Details) - USD ($) $ in Thousands	12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Retiree Medical Plan
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit) [Roll Forward]
Net Prior Service Cost (Credit), beginning of period	$ (13,963)
Annual Amortization	1,756
Net Prior Service Cost (Credit), end of period	(12,207)	$ (13,963)
Amortization of Net (Gain) Loss Calculation
Net (gain) loss	(8,710)	(3,655)
Net (gain) loss subject to amortization	(8,710)	(3,655)
Corridor (10% of greater of APBO or assets)	1,724	1,723
Net (gain)/loss in excess of corridor	$ (6,986)	$ (1,932)
Amortization years	10 years	10 years 9 months 18 days
Other Postretirement Benefit Plans, Defined Benefit Plan Established January 1, 2008 [Member]
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit) [Roll Forward]
Net Prior Service Cost (Credit), beginning of period	$ (962)
Annual Amortization	$ 230
Years Remaining	3 years 2 months 12 days
Curtailment	$ 0
Net Prior Service Cost (Credit), end of period	(732)	$ (962)
Other Postretirement Benefit Plans, Defined Benefit Plan Established July 1, 2012 [Member]
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit) [Roll Forward]
Net Prior Service Cost (Credit), beginning of period	(13,001)
Annual Amortization	$ 1,526
Years Remaining	7 years 6 months
Curtailment	$ 0
Net Prior Service Cost (Credit), end of period	(11,475)	(13,001)
Death Benefit Plan
Amortization of Net (Gain) Loss Calculation
Net (gain) loss	690	690
Net (gain) loss subject to amortization	690	690
Corridor (10% of greater of APBO or assets)	(729)	(729)
Net (gain)/loss in excess of corridor	$ 0	$ 0
Amortization years	7 years 8 months 12 days	8 years 8 months 12 days