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Common Stock - Issued and Outstanding Shares - Additional Information (Detail) - USD ($) |  |  |  |  |  |  |  |  | 3 Months Ended | 9 Months Ended | 49 Months Ended |
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May 27, 2021 | Dec. 07, 2020 | Aug. 06, 2020 | Jul. 01, 2020 | Apr. 28, 2020 | Mar. 12, 2020 | May 22, 2018 | Sep. 14, 2017 | Sep. 30, 2021 | Jun. 30, 2021 | Mar. 31, 2021 | Sep. 30, 2020 | Jun. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, par value |  |  |  |  |  |  |  |  | $ 0.001 |  |  |  |  | $ 0.001 |  | $ 0.001 | $ 0.001
Common stock, shares issued |  |  |  |  |  |  |  |  | 9,453,542 |  |  |  |  | 9,453,542 |  | 9,453,542 | 6,111,735
Proceeds from exercise of warrants |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 339,000 | $ 3,080,000 |  |
Stock option exercises, Shares |  |  |  |  |  |  |  |  | 0 |  |  | 0 |  | 0 | 0 |  |
Restricted stock unit settlements |  |  |  |  |  |  |  |  | 231 |  |  | 236 |  | 231 | 236 |  |
Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, shares issued |  |  |  |  |  |  |  |  |  | 2,149 | 2,965 |  |  |  |  |  |
Restricted stock unit settlements |  |  |  |  |  |  |  |  | 145 |  |  | 128 |  |  |  |  |
April 2020 Private Placement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, shares issued |  |  |  |  | 280,782 |  |  |  |  |  |  |  |  |  |  |  |
Warrants to purchase shares of common stock |  |  |  |  | 0.75 |  |  |  |  |  |  |  |  |  |  |  |
Warrants to purchase shares of common stock, offering price per share |  |  |  |  | $ 6.60 |  |  |  |  |  |  |  |  |  |  |  |
Gross proceeds from issuance of common stock |  |  |  |  | $ 1,900,000 |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from exercise of warrants |  |  |  |  | $ 1,600,000 |  |  |  |  |  |  |  |  |  |  |  |
Percentage of exercise price exceeds in measurement period |  |  |  |  |  |  |  |  |  |  |  |  |  | 300.00% |  |  |
Average daily trading volume for measurement period |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 500,000 |  |  |
Number of required consecutive days weighted average trading price for cancelation or recall of warrants |  |  |  |  |  |  |  |  |  |  |  |  |  | 30 days |  |  |
April 2020 Private Placement [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, shares issued |  |  |  |  |  |  |  |  |  |  |  |  | 280,782 |  |  |  |
April 2020 Private Placement [Member] | Placement Agent [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercise price per unit of warrant |  |  |  |  | $ 7.59 |  |  |  |  |  |  |  |  |  |  |  |
Number of common shares issuable conversion of warrants |  |  |  |  | 25,270 |  |  |  |  |  |  |  |  |  |  |  |
Direct Offering [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross proceeds from issuance of common stock |  |  |  | $ 6,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |
Placement agent fees and offering expenses |  |  |  | 700,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of common stock |  |  |  | $ 5,300,000 |  |  |  |  |  |  |  |  |  |  | $ 5,307,000 |  |
Direct Offering [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, shares issued |  |  |  | 731,707 |  |  |  |  |  |  |  | 731,707 |  |  |  |  |
Common stock, price per share |  |  |  | $ 8.20 |  |  |  |  |  |  |  |  |  |  |  |  |
August 2020 Public Offering [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross proceeds from issuance of common stock |  |  | $ 7,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of common stock |  |  | 6,800,000 |  |  |  |  |  |  |  |  |  |  |  | 6,822,000 |  |
Underwriting discounts and commissions and offering expenses |  |  | $ 700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
August 2020 Public Offering [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, shares issued |  |  | 569,043 |  |  |  |  |  |  |  |  | 569,043 |  |  |  |  |
Common stock, price per share |  |  | $ 10.50 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Underwriters Over-Allotment Option Exercise [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, shares issued | 428,571 | 322,500 | 92,856 |  |  |  |  |  |  |  |  |  |  |  |  |  |
December 2020 Public Offering [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross proceeds from issuance of common stock |  | $ 17,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of common stock |  | 15,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Underwriting discounts and commissions and offering expenses |  | $ 1,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
December 2020 Public Offering [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, shares issued |  | 2,472,500 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, price per share |  | $ 7.00 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
December 2020 Public Offering [Member] | Representative's Warrant [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of common shares issuable conversion of warrants |  | 50,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, price per share |  | $ 8.75 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Adjustments to additional paid in capital Other |  | $ 300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Warrant exercisable term |  | 5 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
May 2021 Public Offering [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross proceeds from issuance of common stock | $ 23,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of common stock | 21,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Underwriting discounts and commissions and offering expenses | $ 1,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
May 2021 Public Offering [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, shares issued | 3,285,714 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, price per share | $ 7.00 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subscription Agreements Executed on April 27, 2020 [Member] | April 2020 Private Placement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercise price per unit of warrant |  |  |  |  |  |  |  |  | $ 7.24 |  |  |  |  | $ 7.24 |  | $ 7.24 |
Subscription Agreements Executed on April 28, 2020 [Member] | April 2020 Private Placement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercise price per unit of warrant |  |  |  |  |  |  |  |  | $ 7.32 |  |  |  |  | $ 7.32 |  | $ 7.32 |
Pre-Funded Warrant [Member] | August 2020 Public Offering [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of common shares issuable conversion of warrants |  |  | 142,857 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-funded warrant, offering price per share |  |  | $ 10.499 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-Funded Warrant [Member] | August 2020 Public Offering [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercise price per unit of warrant |  |  | $ 0.001 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of days of prior notice to achieve not in excess percentage of common stock shares owned by warrant holder |  |  | 61 days |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-Funded Warrant [Member] | August 2020 Public Offering [Member] | Common Stock [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of shares of common stock owned by warrant holder |  |  | 9.99% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-Funded Warrant [Member] | August 2020 Public Offering [Member] | Common Stock [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of shares of common stock owned by warrant holder |  |  | 19.99% |  |  |  |  |  |  |  |  |  |  |  |  |  |
LPC [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock value right to sell, maximum |  |  |  |  |  | $ 11,000,000.0 |  |  |  |  |  |  |  |  |  |  |
Common stock, par value |  |  |  |  |  | $ 0.001 |  |  |  |  |  |  |  |  |  |  |
Minimum percentage of common stock shares outstanding authorized to sell |  |  |  |  |  |  | 20.00% |  |  |  |  |  |  |  |  |  |
Initial purchase of common stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,644 |
Common stock, shares issued |  |  |  |  |  |  |  | 617 |  |  |  |  |  |  |  |  |
Payments related to expense reimbursement |  |  |  |  |  | $ 100,000 |  |  |  |  |  |  |  |  |  |  |
Common stock, shares issued |  |  |  |  |  |  |  |  | 0 |  |  |  |  | 0 |  | 27,868 |
Gross proceeds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 4,400,000 |
Offering expenses |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 500,000 |
Common stock available for sale under offering |  |  |  |  |  |  |  |  | $ 6,600,000 |  |  |  |  | $ 6,600,000 |  | $ 6,600,000 |
LPC [Member] | Purchase Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, purchase price |  |  |  |  |  |  |  | $ 1.00 |  |  |  |  |  |  |  |  |
Additional common stock value right to sell, maximum |  |  |  |  |  |  |  | $ 10,000,000.0 |  |  |  |  |  |  |  |  |
Additional purchase of common stock, maximum |  |  |  |  |  |  |  | 7,500 |  |  |  |  |  |  |  |  |
Offering expenses |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 14,000 |  |
LPC [Member] | Units [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Initial purchase of common stock |  |  |  |  |  |  |  | 1,644 |  |  |  |  |  |  |  |  |
Common stock, purchase price |  |  |  |  |  |  |  | $ 608.00 |  |  |  |  |  |  |  |  |
Purchase agreement, description |  |  |  |  |  |  |  |  |  |  |  |  |  | Unit consisting of (a) one share of our common stock and (b) one warrant to purchase one-quarter of a share of common stock at an exercise price of $699.20 per share, or Warrant. Each Warrant became exercisable six months following the issuance date until the date that is five years and six months after the issuance date and is subject to customary adjustments. |  |  |
Exercise price per unit of warrant |  |  |  |  |  |  |  | $ 699.20 |  |  |  |  |  |  |  |  |
Initial purchase of units consisting of common stock and warrants issued |  |  |  |  |  |  |  | $ 1,000,000.0 |  |  |  |  |  |  |  |  |
LPC [Member] | Other Units [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of warrants issued |  |  |  |  |  |  |  | 0 |  |  |  |  |  |  |  |  |

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