Investments and Fair Value of Financial Instruments - Summary of Changes in Fair Value of Liabilities (Detail) - Level 3 [Member] $ in Thousands |
3 Months Ended |
---|---|
Mar. 31, 2019
USD ($)
| |
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] | |
Balance as of December 31, 2018 | $ 5,083 |
Change in fair value | 8,495 |
Balance as of March 31, 2019 | 13,578 |
Common Stock Warrant Liability [Member] | Purchase Agreement [Member] | |
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] | |
Balance as of December 31, 2018 | 2,354 |
Change in fair value | 3,970 |
Balance as of March 31, 2019 | 6,324 |
Common Stock Warrant Liability [Member] | June 2018 Offering [Member] | |
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] | |
Balance as of December 31, 2018 | 2,729 |
Change in fair value | 4,525 |
Balance as of March 31, 2019 | $ 7,254 |