Accounts Receivable - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Accounts Receivable Textual [Abstract]
Accounts receivable unbilled amounts	$ 3.4	$ 2.7

Amount of unbilled receivables under long-term contracts that have not been billed and were not billable.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 910
-SubTopic 310
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=68065756&loc=d3e49336-109356

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