Preferred Stock, Common Stock and Stockholders' Equity - Warrants - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended					12 Months Ended
	Sep. 30, 2018	Feb. 28, 2017	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Sale Of Stock [Line Items]
Weighted average exercise price of warrants				$ 3.46				$ 2.91	$ 3.46
Change in fair value of warrant liability			$ 433,392	$ 2,349,624	$ (1,544,138)	$ 1,261,912	$ (3,072,747)	$ 433,392	$ (1,005,349)
July 2016 Financing [Member]
Sale Of Stock [Line Items]
Unregistered warrants to purchase of common stock		526,315
Conversion of stock, shares issued		211,860
Weighted average exercise price of warrants		$ 2.41
Reclassification of warrant liability to Additional Paid-in Capital		$ 1,400,000
Warrant Amendments [Member]
Sale Of Stock [Line Items]
Unregistered warrants to purchase of common stock								2,449,129
Reclassification of warrant liability to Additional Paid-in Capital								$ 3,300,000
Change in fair value of warrant liability								$ 433,000
Amendment date								2018-03
Underwriters [Member]
Sale Of Stock [Line Items]
Unregistered warrants to purchase of common stock expired	84,000