Nature of Business and Basis of Presentation - Additional Information (Detail) - Merger Agreement [Member]	6 Months Ended
Jun. 30, 2018
Business And Basis Of Presentation [Line Items]
Agreement of reorganization and merger date	Jan. 18, 2017
Merger Sub Corp I Inc and Mustang Merger Sub II LLC [Member]
Business And Basis Of Presentation [Line Items]
Business acquisition, percentage of voting interest acquired	100.00%

Percentage of voting equity interests acquired at the acquisition date in the business combination.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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