Fair Value Measurements - Schedule of Fair Value of Financial Assets Measured on Recurring Basis (Detail) - Fair Value Measurements Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financial Assets
Total financial assets	$ 146,540	$ 105,524
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
Money Market Funds [Member]
Financial Assets
Total financial assets	146,240	105,224
Restricted Money Market Funds [Member]
Financial Assets
Total financial assets	300	300
Level 1 [Member]
Financial Assets
Total financial assets	146,540	105,524
Level 1 [Member] | Money Market Funds [Member]
Financial Assets
Total financial assets	146,240	105,224
Level 1 [Member] | Restricted Money Market Funds [Member]
Financial Assets
Total financial assets	300	$ 300
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