Summary of Significant Accounting Policies - Goodwill (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Dec. 31, 2015	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016
Goodwill and Intangible Asset Impairment		$ 0
Goodwill, Gross		1,085,855	$ 1,085,420	$ 1,082,540
Goodwill, Accumulated Impairment Loss		784,053	784,053	784,053
Goodwill		301,802	301,367	298,487
Goodwill, Period Increase (Decrease)		435	2,880
Industrial [Member]
Goodwill, Written off Related to Sale of Business Unit				(1,100)
Goodwill, Gross		411,458	410,694	408,705
Goodwill, Accumulated Impairment Loss		(137,204)	(137,204)	(137,204)
Goodwill		274,254	273,490	271,501
Goodwill, Period Increase (Decrease)		764	1,989
Infrastructure [Member]
Goodwill, Written off Related to Sale of Business Unit				(6,500)
Goodwill and Intangible Asset Impairment	$ 106,100
Goodwill, Gross		633,211	633,211	633,211
Goodwill, Accumulated Impairment Loss		(633,211)	(633,211)	(633,211)
Goodwill		0	0	$ 0
Goodwill, Period Increase (Decrease)		$ 0	$ 0
Goodwill, Impairment Loss	(105,700)
Trademarks [Member] \| Industrial [Member]
Impairment of Intangible Assets (Excluding Goodwill)	2,300
Trademarks [Member] \| Infrastructure [Member]
Impairment of Intangible Assets (Excluding Goodwill)	$ 400

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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