Income Taxes - Components of the Temporary Differences (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2017
Deferred Tax Assets: [Abstract]
Postretirement benefits	$ 20,775	$ 18,862
Accrued liabilities	5,042	4,754
Net operating loss carryforward	37,768	32,552
Other	5,950	6,728
Total deferred tax assets	69,535	62,896
Deferred tax liabilities: [Abstract]
Fixed assets	(15,562)	(16,156)
Other	(3,749)	(5,536)
Total deferred tax liabilities	(19,311)	(21,692)
Valuation allowance	(52,019)	(1,896)	$ (1,613)
Deferred tax assets, net		$ 39,308
Deferred Tax Liabilities, Net	$ (1,795)