Income Taxes - Components of the Temporary Differences (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2015
Deferred Tax Assets: [Abstract]
Postretirement benefits	$ 30,253	$ 33,273	$ 31,100
Accrued liabilities	7,885	11,760	10,091
Net operating loss carryforward	38,985	38,196	41,544
Intangible assets	0	71	594
Other	6,824	6,881	6,794
Total deferred tax assets	83,947	90,181	90,123
Deferred tax liabilities: [Abstract]
Unrealized gain on investments	0	(609)	(2,242)
Fixed assets	(17,096)	(5,370)	(2,647)
Other	(2,181)	(1,789)	(1,943)
Total deferred tax liabilities	(19,277)	(7,768)	(6,832)
Valuation allowance	(1,615)	(1,627)	(84,857)
Net deferred tax assets (liabilities)	$ 63,055	$ 80,786
Net deferred tax assets (liabilities)			$ (1,566)