Fair Value of Financial Instruments - Summary of Financial Instruments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Liabilities
Contingent liability for Essentialis purchase price	$ 10,138	$ 5,938
2017 PIPE Warrant Liability [Member]
Liabilities
Warrant liability	4,777	10,822
2018 PIPE Warrant Liability [Member]
Liabilities
Warrant liability	867	1,354
Fair Value, Measurements, Recurring [Member]
Liabilities
Total common stock warrant and contingent consideration liability	15,782	18,114
Fair Value, Measurements, Recurring [Member] | Derivative Financial Instruments, Liabilities | 2017 PIPE Warrant Liability [Member]
Liabilities
Warrant liability	4,777	10,822
Fair Value, Measurements, Recurring [Member] | Derivative Financial Instruments, Liabilities | 2018 PIPE Warrant Liability [Member]
Liabilities
Warrant liability	867	1,354
Essentialis, Inc. [Member] | Fair Value, Measurements, Recurring [Member]
Liabilities
Contingent liability for Essentialis purchase price	10,138	5,938
Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Liabilities
Total common stock warrant and contingent consideration liability	15,782	18,114
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Financial Instruments, Liabilities | 2017 PIPE Warrant Liability [Member]
Liabilities
Warrant liability	4,777	10,822
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Financial Instruments, Liabilities | 2018 PIPE Warrant Liability [Member]
Liabilities
Warrant liability	867	1,354
Level 3 [Member] | Essentialis, Inc. [Member] | Fair Value, Measurements, Recurring [Member]
Liabilities
Contingent liability for Essentialis purchase price	$ 10,138	$ 5,938