Amount of gain (loss) on sale or disposal of assets, including but not limited to property plant and equipment, intangible assets and equity in securities of subsidiaries or equity method investee.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2443-110228

Name:	us-gaap_GainLossOnDispositionOfAssets1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Subsequent Events - Additional Information (Detail) - USD ($) $ in Millions	Feb. 12, 2018	Dec. 31, 2017
CFO
Subsequent Event [Line Items]
Severance payable		$ 3.7
Subsequent Event
Subsequent Event [Line Items]
Gain from sale of office property	$ 6.7
Subsequent Event \| Chairman
Subsequent Event [Line Items]
Sale of office property	$ 9.7