Stockholders' Equity - Additional Information (Detail) $ / shares in Units, $ in Millions					12 Months Ended
	Dec. 05, 2017 USD ($) $ / shares shares	Mar. 24, 2017 $ / shares shares	Oct. 28, 2016 $ / shares shares	Aug. 04, 2015 Vote $ / shares	Dec. 31, 2017 USD ($) Vote $ / shares shares	Dec. 31, 2016 $ / shares shares	Jul. 29, 2015 $ / shares shares
Class Of Stock [Line Items]
Preferred stock, shares authorized | shares							50,000,000
Preferred stock par value							$ 0.01
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.
Change in fair value of consideration warrants expense | $					$ 0.2
Loan and Security Agreement [Member] | Horizon Technology Finance Corporation and Silicon Valley Bank [Member]
Class Of Stock [Line Items]
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
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 | shares			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]
Class Of Stock [Line Items]
Warrants to purchase shares of common stock | shares		38,006
Exercise price of warrants		$ 5.92
Warrant shares percentage issued of loan amount		3.00%	3.00%
Letter Agreement [Member] | M&F Group [Member]
Class Of Stock [Line Items]
Warrants expiration date					Dec. 05, 2024
Class A Common Stock [Member]
Class Of Stock [Line Items]
Common stock, shares authorized | shares					100,000,000	100,000,000	100,000,000
Common stock par value					$ 0.01	$ 0.01	$ 0.01
Common stock, vote per share | Vote				1	1
Class A Common Stock [Member] | Letter Agreement [Member] | M&F Group [Member]
Class Of Stock [Line Items]
Share price	$ 4.38
Aggregate amount of common stock may be sold | $	$ 10.0
Warrants to purchase shares of common stock | shares	198,267
Exercise price of warrants	$ 5.04
Percentage of warrants exercisable	115.00%
Class B Common Stock [Member]
Class Of Stock [Line Items]
Common stock, shares authorized | shares					100,000,000	100,000,000	100,000,000
Common stock par value				$ 0.01	$ 0.01	$ 0.01	$ 0.01
Common stock, vote per share | Vote				1	1