Fair Value Measurements - Schedule of Fair Value of Financial Assets Measured on Recurring Basis (Detail) - Fair Value Measurements Recurring [Member] - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financial Assets
Total financial assets	$ 106,577	$ 146,540
Financial Liabilities
Total financial liabilities		56,420
Warrant liabilities [Member]
Financial Liabilities
Total financial liabilities		45,935
Securities issuance obligation [Member]
Financial Liabilities
Total financial liabilities		10,485
Level 1 [Member]
Financial Assets
Total financial assets	106,577	146,540
Level 3 [Member]
Financial Liabilities
Total financial liabilities		56,420
Level 3 [Member] | Warrant liabilities [Member]
Financial Liabilities
Total financial liabilities		45,935
Level 3 [Member] | Securities issuance obligation [Member]
Financial Liabilities
Total financial liabilities		10,485
Money Market Funds [Member]
Financial Assets
Total financial assets	106,277	146,240
Money Market Funds [Member] | Level 1 [Member]
Financial Assets
Total financial assets	106,277	146,240
Restricted Money Market Funds [Member]
Financial Assets
Total financial assets	300	300
Restricted Money Market Funds [Member] | Level 1 [Member]
Financial Assets
Total financial assets	$ 300	$ 300