License and Development Agreements - Endo License and Development Agreement - Additional Information (Detail) - USD ($)	1 Months Ended			12 Months Ended
	Jan. 31, 2017	Nov. 30, 2015	Feb. 28, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Oct. 31, 2015	Oct. 26, 2015
Revenue Recognition, Milestone Method [Line Items]
Potential payments upon filing and acceptance			$ 10,000,000
Potential milestone payment receivable upon regulatory approval								$ 50,000,000
Milestone payment upon regulatory approval deferred for future revenue recognition		$ 20,000,000
Patent extension starting period				2020
Patent extension ending period				2027
Royalty payment description				$50 million upon regulatory approval, earned in October 2015 and received in November 2015. Of the $50 million received in November 2015, $20 million related to a patent extension and was recorded as deferred revenue because all or a portion of such $20 million was contingently refundable to Endo if a third party generic product was introduced in the U.S. during the patent extension period from 2020 to 2027. However, due to the Company and Endo entering into a Termination Agreement on December 7, 2016 which terminated the BELBUCA® license to Endo effective January 6, 2017, the deferred $20 million was recognized as revenue during the nine months ended September 30, 2017 in the accompanying condensed consolidated statement of operations (see note 7, Business Combination and Asset Acquisition).
Deferred revenue from research and development activities				$ 799,000	$ 1,134,000	$ 909,000
Milestone payment, deferred revenue				0	1,700,000
Endo Agreement [Member]
Revenue Recognition, Milestone Method [Line Items]
Deferred revenue from research and development activities				0	$ 0	900,000
Endo Agreement [Member] | BELBUCA [Member]
Revenue Recognition, Milestone Method [Line Items]
Potential milestone payment receivable upon regulatory approval									$ 50,000,000
Milestone payment upon regulatory approval deferred for future revenue recognition	$ 20,000,000
Deferred revenue from research and development activities							$ 6,000,000
Milestone payment, deferred revenue		$ 20,000,000
Milestone payment recognized						$ 30,000,000
Endo Agreement [Member]
Revenue Recognition, Milestone Method [Line Items]
Deferred revenue refund payment				$ 20,000,000
Termination agreement date				Dec. 07, 2016
License termination effective date				Jan. 06, 2017