Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) Candidate	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of VDA drug candidates tested | Candidate			2
Accumulated deficit	$ (286,305)		$ (286,305)		$ (278,463)
Cash and cash equivalents	5,004	$ 7,939	5,004	$ 7,939	$ 3,535	$ 27,285
Net loss	$ (3,884)	$ (3,641)	$ (7,842)	$ (6,966)
Substantial doubt about going concern, management's evaluation			The Company’s existing cash and cash equivalents to support its operations only into October 2017. Prior to this time, the Company will need to secure additional funding or it could be forced to curtail or terminate its drug development programs and its operations. Because the Company does not currently have a source of working capital that will sustain its planned operations past October 2017, Management has determined that there is substantial doubt about the Company’s ability to continue as a going concern.
Substantial doubt about going concern			Any additional equity financing, if available, may not be available on favorable terms and would most likely be dilutive to current stockholders.