Nature of Business and Basis of Presentation - Additional Information (Detail) - USD ($)		9 Months Ended
	Mar. 09, 2017	Sep. 30, 2017	Mar. 31, 2017	Jan. 31, 2017
Business And Basis Of Presentation [Line Items]
Shares of common stock called by warrants			49,776
Warrants exercise price per share		$ 2.70	$ 0.01
Merger Agreement [Member]
Business And Basis Of Presentation [Line Items]
Agreement of reorganization and merger date		Jan. 18, 2017
Merger Agreement [Member] | Merger Sub Corp I Inc and Mustang Merger Sub II LLC [Member]
Business And Basis Of Presentation [Line Items]
Business acquisition, percentage of voting interest acquired		100.00%
Convertible Promissory Note Purchase Agreement [Member] | 6% Convertible Notes [Member]
Business And Basis Of Presentation [Line Items]
Notes payable				$ 8,600,000
Notes payable, interest rate				6.00%
Description of second closing		The second closing was included in the sale of Series B redeemable convertible preferred stock (“redeemable preferred stock”) that closed on August 16, 2017 (see Note 9).
Convertible Promissory Note Purchase Agreement [Member] | 6% Convertible Notes [Member] | Convertible Promissory Note Purchase Agreement Initial Closing [Member]
Business And Basis Of Presentation [Line Items]
Gross proceeds from notes payable	$ 3,150,630
Notes payable modified and replaced with convertible notes	196,496
Accrued expenses modified and replaced with convertible notes	$ 881,044