Unaudited Quarterly Financial Data (Narrative) (Detail) - USD ($) $ in Thousands	3 Months Ended						12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016
Effect of Fourth Quarter Events [Line Items]
Environmental remediation charge							$ 1,822	$ 903	$ 1,313
Impairment charges		$ 256,266					256,266
Immaterial correction of an error				$ 3,139
Deferred tax assets valuation allowance	$ 77,416			$ 773			77,416	773
Income (loss) before income taxes		(267,985)					(292,822)	$ 17,361	$ 53,854
Adjustment
Effect of Fourth Quarter Events [Line Items]
Income (loss) before income taxes		$ (71,350)
U.S.
Effect of Fourth Quarter Events [Line Items]
Deferred tax assets valuation allowance	76,500						$ 76,500
Arsynco, Inc
Effect of Fourth Quarter Events [Line Items]
Environmental remediation charge	$ 920		$ 902		$ 733	$ 170