Basic and Diluted Net (Loss) Income Per Share - Summary of Number of Participating Securities and Earning Allocated to those Securities (Detail) - USD ($) shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Earnings allocated to participating shareholders		$ 0.5	$ 1.2
Number of participating securities	1.1	1.0	1.0

Amount of undistributed earnings (loss) allocated to participating securities for the diluted earnings (loss) per share or per unit calculation under the two-class method.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=96947427&loc=SL5780133-109256

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