Investments and Fair Value Instruments - Summary of Changes in Fair Value and Other Adjustments of Liabilities (Detail) - Level 3 [Member] - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 16,936	$ 8,083
Change in fair value and other adjustments	(6,570)	8,243
Exercise of warrants	(5,659)	(7,016)
ISI acquisition contingent consideration	280	0
Ending Balance	4,987	16,936
Common Stock Warrant Liability [Member] \| Purchase Agreement [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	4,579	2,354
Change in fair value and other adjustments	(2,277)	2,225
Exercise of warrants	(1,641)	0
ISI acquisition contingent consideration	0	0
Ending Balance	662	4,579
Common Stock Warrant Liability [Member] \| June 2018 Offering [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	5,444	2,729
Change in fair value and other adjustments	(1,426)	2,715
Exercise of warrants	(4,018)	0
ISI acquisition contingent consideration	0	0
Ending Balance	0	5,444
Common Stock Warrant Liability [Member] \| June 2019 Offering [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	1,993	0
Common stock and warrants issued		4,198
Change in fair value and other adjustments	(1,161)	4,811
Exercise of warrants	0	(7,016)
ISI acquisition contingent consideration	0	0
Ending Balance	832	1,993
Common Stock Warrant Liability [Member] \| September 2019 Offering [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	2,920	0
Common stock and warrants issued		3,428
Change in fair value and other adjustments	(1,706)	(508)
Exercise of warrants	0	0
ISI acquisition contingent consideration	0	0
Ending Balance	1,214	2,920
Contingent Liabilities [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	2,000	3,000
Change in fair value and other adjustments	0	(1,000)
Exercise of warrants	0	0
ISI acquisition contingent consideration	280	0
Ending Balance	$ 2,280	$ 2,000

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- Definition

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

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No definition available.

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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.

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- Definition

Amount of issuances 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
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-Topic 820
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-Section 50
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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
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-Section 50
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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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