Financial Instruments and Fair Value Measurements - Summary of Financial Instruments Not Carried at Fair Value (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash, cash equivalents and restricted cash, Fair value	$ 128,371	$ 102,941
Noncontrolling interest in subsidiary	19,177	17,756
Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash, cash equivalents and restricted cash, Carrying amount	128,371	102,941
Carrying Amount \| CompX
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Noncontrolling interest in subsidiary	19,177	17,756
Fair Value \| CompX
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Noncontrolling interest in subsidiary	$ 22,854	$ 22,224

Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3521-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3044-108585

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=98513485&loc=SL98516268-108586

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