Costs and Estimated Earnings on Uncompleted Contracts - Additional Information (Detail) - USD ($)	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Costs In Excess Of Billings On Uncompleted Contracts Or Programs [Abstract]
Provision for estimated losses on uncompleted contracts	$ 0	$ 0

Losses recognized in the current period on contracts which are expected to generate losses, which are probable and can be reasonably estimated, in a future period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.2)
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 35
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=68068069&loc=d3e57763-111642

Name:	us-gaap_LossOnContracts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration