Changes to Accrued Cease-Use Liability (Parenthetical) (Detail) - USD ($)	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Lease Commitments And Contingencies [Line Items]
Increase in deferred rent	$ (114,000)	$ (64,000)
Sublease
Lease Commitments And Contingencies [Line Items]
Increase in deferred rent	$ 200,000	$ 246,000

Change during the period in carrying value for all deferred liabilities due within one year or operating cycle.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

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