Equity Method Investments - Summary of ASV Financial Information (Parenthetical) (Detail)	Feb. 26, 2018	Dec. 31, 2017	Jun. 30, 2017
ASV after transaction [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment ownership percentage	21.20%	21.22%	21.20%

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant