Investments and Fair Value of Financial Instruments - Summary of Changes in Fair Value of Liabilities (Detail) - Level 3 [Member] $ in Thousands	9 Months Ended
Sep. 30, 2020 USD ($)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance as of December 31, 2019	$ 16,936
Change in fair value	(6,212)
Exercise of warrants (Note 10)	(5,659)
ISI acquisition contingent consideration	280
Balance as of September 30, 2020	5,345
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, 2019	4,579
Change in fair value	(2,155)
Exercise of warrants (Note 10)	(1,641)
ISI acquisition contingent consideration	0
Balance as of September 30, 2020	783
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, 2019	5,444
Change in fair value	(1,426)
Exercise of warrants (Note 10)	(4,018)
ISI acquisition contingent consideration	0
Balance as of September 30, 2020	0
Common Stock Warrant Liability [Member] \| June 2019 Offering [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance as of December 31, 2019	1,993
Change in fair value	(1,064)
Exercise of warrants (Note 10)	0
ISI acquisition contingent consideration	0
Balance as of September 30, 2020	929
Common Stock Warrant Liability [Member] \| September 2019 Offering [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance as of December 31, 2019	2,920
Change in fair value	(1,567)
Exercise of warrants (Note 10)	0
ISI acquisition contingent consideration	0
Balance as of September 30, 2020	1,353
Contingent Liability [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance as of December 31, 2019	2,000
Change in fair value	0
Exercise of warrants (Note 10)	0
ISI acquisition contingent consideration	280
Balance as of September 30, 2020	$ 2,280

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- Definition

Fair value measurement with unobservable inputs reconciliation recurring basis liability warrants exercisable.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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- Definition

Amount of increase (decrease) of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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