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.

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Goodwill - Additional Information (Detail) - USD ($)		12 Months Ended
Goodwill - Additional Information (Detail) - USD ($)	Sep. 30, 2008	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Goodwill impairment charge		$ 0	$ 0	$ 0
Goodwill, gross		33,600,000
Goodwill		$ 23,742,000	$ 23,742,000
Marine Components
Goodwill [Line Items]
Goodwill impairment charge	$ 9,900,000