Technology, License and Distribution Agreements - Additional Information (Detail) $ in Thousands		1 Months Ended				3 Months Ended		9 Months Ended		12 Months Ended
	Aug. 01, 2016 USD ($)	Jan. 31, 2017 USD ($)	Mar. 31, 2016 Country	Jul. 31, 2015 USD ($)	Sep. 30, 2010 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Long-term Purchase Commitment [Line Items]
Pre-existing relationship, settlement gain							$ 80,229		$ 80,229
Net product sales						$ 18,768	$ 5,241	$ 61,041	$ 8,176
Contrave
Long-term Purchase Commitment [Line Items]
Payment for acquisition	$ 60,000	$ 15,000
Takeda Pharmaceutical Company Limited
Long-term Purchase Commitment [Line Items]
Potential milestone payment, one	10,000
Potential milestone payment, two	20,000
Potential milestone payment, three	30,000
Potential milestone payment, four	50,000
Annual net sales milestones, one	200,000
Annual net sales milestones, two	300,000
Annual net sales milestones, three	400,000
Annual net sales milestones, four	600,000
Pre-existing relationship, settlement gain	$ 80,200
Collaborative Arrangement
Long-term Purchase Commitment [Line Items]
Percentage of expenses responsible				25.00%
Collaborative Arrangement | Takeda Pharmaceutical Company Limited
Long-term Purchase Commitment [Line Items]
Upfront payment received					$ 50,000
Additional payments eligible					1,000,000
Amount achievable between execution of collaboration agreement and first commercial sale					$ 100,000
Tiered royalty payments, Minimum					20.00%
Tiered royalty payments, Maximum					35.00%
Percentage of responsible costs for the terminated Light Study				100.00%
Percentage of expenses responsible				75.00%
Additional payments eligible				$ 105,000
Pre-existing relationship, settlement gain										$ 80,200
Distribution Agreement | Kwang Dong Pharmaceutical Company Limited
Long-term Purchase Commitment [Line Items]
Net product sales								3,300
Commercialization and Distributorship Agreement | Laboratorios Farmaceuticos Rovi, S.A.
Long-term Purchase Commitment [Line Items]
Net product sales								1,800
Commercialization and Distributorship Agreement | Valeant Pharmaceuticals Ireland
Long-term Purchase Commitment [Line Items]
Net product sales								$ 2,000
Commercialization and Distributorship Agreement | Valeant Pharmaceuticals Ireland | Central and Eastern Europe
Long-term Purchase Commitment [Line Items]
Number of countries for commercialization activities | Country			19