Fair Value Measurements - Summary of Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Liabilities:
Warrant liabilities	$ 32,767	$ 41,549
Recurring
Assets:
Total	30,574	50,401
Liabilities:
Warrant liabilities	32,767	41,549
Total	32,767	41,549
Recurring | (Level 1)
Assets:
Total	30,574	50,401
Liabilities:
Warrant liabilities	0	0
Total	0
Recurring | (Level 2)
Assets:
Total	0	0
Liabilities:
Warrant liabilities	0	0
Total	0	0
Recurring | (Level 3)
Assets:
Total	0	0
Liabilities:
Warrant liabilities	32,767	41,549
Total	32,767	41,549
Recurring | Money market funds
Assets:
Cash and cash equivalents, fair value disclosure	30,574	50,401
Recurring | Money market funds | (Level 1)
Assets:
Cash and cash equivalents, fair value disclosure	30,574	50,401
Recurring | Money market funds | (Level 2)
Assets:
Cash and cash equivalents, fair value disclosure	0	0
Recurring | Money market funds | (Level 3)
Assets:
Cash and cash equivalents, fair value disclosure	$ 0	$ 0