Stockholders' Equity - Additional Information (Detail)							12 Months Ended
	May 04, 2021 shares	Dec. 08, 2020 USD ($) $ / shares shares	Nov. 24, 2020 USD ($) $ / shares shares	Apr. 30, 2020 USD ($) $ / shares	Mar. 24, 2017 $ / shares shares	Oct. 28, 2016 $ / shares shares	Dec. 31, 2021 USD ($) Vote $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($)	Jun. 25, 2021 USD ($)	Jan. 14, 2021 USD ($)	Jul. 29, 2015 $ / shares shares
Class Of Stock [Line Items]
Preferred stock, shares authorized												50,000,000
Preferred stock par value | $ / shares												$ 0.01
Capital stock, shares authorized	350,000,000							250,000,000
Common stock, voting rights							Holders of Class A Common Stock and Class B Common Stock will be entitled to one vote for each share held on all matters submitted to stockholders for their vote or approval.
Net proceeds from issuance of common stock | $							$ 26,757,000	$ 14,426,000	$ 5,443,000
Issuance of Class A Common Stock under LPC Agreement | $							9,087,000	1,930,000
Change in fair value of consideration warrants expense | $							1,600,000	(300,000)	$ 800,000
Loan and Security Agreement [Member] | Horizon Technology Finance Corporation and Silicon Valley Bank [Member]
Class Of Stock [Line Items]
Warrants expiration period						7 years
Loan and Security Agreement [Member] | Horizon Technology Finance Corporation and Silicon Valley Bank [Member] | Tranche One [Member]
Class Of Stock [Line Items]
Warrants to purchase shares of common stock						152,580
Exercise price of warrants | $ / shares						$ 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]
Class Of Stock [Line Items]
Warrants to purchase shares of common stock					38,006
Exercise price of warrants | $ / shares					$ 5.92
Warrant shares percentage issued of loan amount					3.00%	3.00%
Cantor Fitzgerald [Member] | ATM Offering [Member]
Class Of Stock [Line Items]
Gross proceeds from issuance of common stock | $							18,200,000	13,000,000.0
Net proceeds from issuance of common stock | $							$ 17,700,000	$ 12,500,000
LPC Purchase Agreement [Member]
Class Of Stock [Line Items]
Agreement term			36 months
Class A Common Stock [Member]
Class Of Stock [Line Items]
Common stock, shares authorized	200,000,000						200,000,000	100,000,000				100,000,000
Common stock par value | $ / shares							$ 0.01	$ 0.01				$ 0.01
Increase in shares authorized	100,000,000
Common stock, vote per share | Vote							1
Common stock, shares outstanding							66,942,777	54,050,710
Class A Common Stock [Member] | Cantor Fitzgerald [Member] | ATM Offering [Member]
Class Of Stock [Line Items]
Common stock par value | $ / shares				$ 0.01
Aggregate offering price | $										$ 50,000,000.0	$ 5,500,000
Shares sold							8,929,147	5,480,941
Class A Common Stock [Member] | Cantor Fitzgerald [Member] | ATM Offering [Member] | Maximum [Member]
Class Of Stock [Line Items]
Aggregate offering price | $				$ 13,000,000.0
Class A Common Stock [Member] | LPC Purchase Agreement [Member]
Class Of Stock [Line Items]
Shares sold		963,855	425,725
Shares registered under the LPC agreement		5,331,306
Percentage of aggregate offering price			1.50%
Share price | $ / shares		$ 2.08
Aggregate gross purchase price | $		$ 2,000,000.0
Issuance of Class A Common Stock under LPC agreement shares							3,941,726
Issuance of Class A Common Stock under LPC Agreement | $							$ 9,100,000
Maximum obligation for number of shares issued per day			2,000,000
Purchase price for shares			The purchase price for shares of Class A common stock to be purchased by Lincoln Park under a Regular Purchase will be equal to the lower of (in each case, subject to the adjustments described in the LPC Purchase Agreement): (i) the lowest sale price for the Class A common stock on the applicable purchase date and (ii) the arithmetic average of the three lowest closing sales prices for the Class A common stock during the 10 consecutive trading days prior to the purchase date
Common stock, shares outstanding			73,880,351
Class A Common Stock [Member] | LPC Purchase Agreement [Member] | Maximum [Member]
Class Of Stock [Line Items]
Aggregate offering price | $			$ 47,000,000
Class A Common Stock [Member] | LPC Purchase Agreement [Member] | Regular Purchase Share Limit [Member] | Maximum [Member]
Class Of Stock [Line Items]
Number of shares issued per day			250,000
Class A Common Stock [Member] | LPC Purchase Agreement [Member] | Regular Purchase Share Limit Two [Member] | Maximum [Member]
Class Of Stock [Line Items]
Increase in number of shares issued per day			275,000
Class A Common Stock [Member] | LPC Purchase Agreement [Member] | Regular Purchase Share Limit Two [Member] | Minimum [Member]
Class Of Stock [Line Items]
Share price | $ / shares			$ 4.00
Class A Common Stock [Member] | LPC Purchase Agreement [Member] | Regular Purchase Share Limit Three [Member] | Maximum [Member]
Class Of Stock [Line Items]
Increase in number of shares issued per day			300,000
Class A Common Stock [Member] | LPC Purchase Agreement [Member] | Regular Purchase Share Limit Three [Member] | Minimum [Member]
Class Of Stock [Line Items]
Share price | $ / shares			$ 5.00
Class A Common Stock [Member] | LPC Purchase Agreement [Member] | Additional Accelerated [Member]
Class Of Stock [Line Items]
Percentage of number of shares issued during period							300.00%
Percentage of number of common stock shares traded during period							30.00%
Class A Common Stock [Member] | LPC Purchase Agreement [Member] | Additional Accelerated [Member] | Maximum [Member]
Class Of Stock [Line Items]
Share price as a percentage of the volume weighted average price							97.00%
Class A Common Stock [Member] | LPC Purchase Agreement [Member] | Exchange Cap [Member] | Maximum [Member]
Class Of Stock [Line Items]
Maximum number of shares to be issued as percentage of outstanding			19.99%
Maximum number of shares to be issued			14,768,682
Class A Common Stock [Member] | Lincoln Park Capital Fund, LLC and Affiliates [Member] | Maximum [Member]
Class Of Stock [Line Items]
Ownership percentage by noncontrolling owners			9.99%
Class B Common Stock [Member]
Class Of Stock [Line Items]
Common stock, shares authorized							100,000,000	100,000,000				100,000,000
Common stock par value | $ / shares							$ 0.01	$ 0.01				$ 0.01
Common stock, vote per share | Vote							1
Common stock, shares outstanding							23,093,860	23,094,221
Common Stock [Member]
Class Of Stock [Line Items]
Common stock, shares authorized	300,000,000							200,000,000