Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Jun. 30, 2018
Project Unapproved Change Orders and Claims [Line Items]
Unapproved change orders and claims	$ 13.2	$ 15.0

Amount of cost incurred on construction contract for unapproved change order, claim, or similar item subject to uncertainty.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 910
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6471471&loc=d3e48698-109348

Name:	us-gaap_UnapprovedChangeOrdersAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant