Employee Benefit Plans - Components of Net Periodic Benefit Costs (Details) - Other Postretirement Benefits Plan - USD ($) $ in Thousands	12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016
Defined Benefit Plan Disclosure
Service cost	$ 609	$ 760	$ 1,388
Interest cost	835	829	1,194
Amortization of net gain	(841)	(630)	(196)
Amortization of prior service credit	(1,757)	(1,757)	(1,757)
Net periodic benefit cost	$ (1,154)	$ (798)	$ 629