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Notes Payable - Additional Information (Detail) - USD ($)			1 Months Ended		12 Months Ended
	Mar. 24, 2017	Oct. 28, 2016	Mar. 31, 2017	Oct. 31, 2016	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Loan borrowed amount					$ 887,000	$ 500,000	$ 500,000
Loan and Security Agreement [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate floor				0.50%
Loan and Security Agreement [Member] \| Horizon Technology Finance Corporation and Silicon Valley Bank [Member]
Debt Instrument [Line Items]
Loan borrowed amount				$ 20,000,000.0
Debt instrument, interest rate floor				10.50%
Variable rate basis							one-month LIBOR
Interest rate description					Each loan tranche bore interest at a floating rate equal to 10.5% plus the amount by which the one-month LIBOR exceeds 0.5%.
Warrant exercise price condition					exercise price equal to the lower of (a) the volume weighted average price per share of the Company’s Class A Common Stock, as reported on the principal stock exchange on which the Company’s Class A Common Stock is listed, for 10 trading days prior to the issuance of the applicable Warrants or (b) the closing price of a share of the Company’s Class A Common Stock on the trading day prior to the issuance of the applicable Warrants
Warrants expiration period		7 years
Interest expense related to loan agreement					$ 0	$ 700,000	$ 1,800,000
Loan agreement termination period					2020-12
Loan and Security Agreement [Member] \| Horizon Technology Finance Corporation and Silicon Valley Bank [Member] \| Tranche One [Member]
Debt Instrument [Line Items]
Loan borrowed amount				$ 12,500,000
Debt instrument, payment terms					The Company borrowed the first tranche of $12.5 million upon close of the Loan Agreement in October 2016. The first tranche required only monthly interest payments until May 1, 2018, followed by equal monthly payments of principal plus accrued interest through the scheduled maturity date on May 1, 2020.
Debt instrument, final payment				$ 800,000
Debt instrument, maturity date				May 01, 2020
Debt instrument, frequency of periodic Payment					monthly
Warrants to purchase shares of common stock		152,580
Exercise price of warrants		$ 6.39
Warrant shares percentage issued of loan amount		6.00%
Loan and Security Agreement [Member] \| Horizon Technology Finance Corporation and Silicon Valley Bank [Member] \| Tranche Two [Member]
Debt Instrument [Line Items]
Loan borrowed amount			$ 7,500,000
Debt instrument, payment terms					The Company borrowed the second tranche of $7.5 million in March 2017. The second tranche requires only monthly interest payments until October 1, 2018, followed by equal monthly payments of principal plus accrued interest through the scheduled maturity date on October 1, 2020.
Debt instrument, final payment				$ 500,000
Debt instrument, maturity date				Oct. 01, 2020
Debt instrument, frequency of periodic Payment					monthly
Warrants to purchase shares of common stock	38,006
Exercise price of warrants	$ 5.92
Warrant shares percentage issued of loan amount	3.00%	3.00%
Loan and Security Agreement [Member] \| Horizon Technology Finance Corporation and Silicon Valley Bank [Member] \| Tranche One And Two [Member]
Debt Instrument [Line Items]
Debt instrument, payment terms					The total amount of the payment was increased to $0.8 million as a result of the Second and Third Amendments. For each of the first and second tranches, the combined Second and Third Amendment required only monthly interest payments on the outstanding principal balance for the amounts due from April 1, 2020, through August 1, 2020.
Debt instrument, final payment					$ 800,000