Stock-Based Compensation and Warrants - Additional Information (Detail)			1 Months Ended	3 Months Ended		6 Months Ended	9 Months Ended
	May 20, 2015 shares	May 14, 2015	Dec. 31, 2013 $ / shares shares	Sep. 30, 2018 USD ($) $ / shares shares	Sep. 30, 2017 USD ($)	Jun. 30, 2014 $ / shares shares	Sep. 30, 2018 USD ($) IncentivePlan $ / shares shares	Sep. 30, 2017 USD ($)	Dec. 31, 2017 shares
Share-based Compensation Arrangement by Share-based Payment Award and Warrants [Line Items]
Number of equity incentive plans | IncentivePlan							2
Total number of options outstanding				525,194			525,194		288,129
Unrecognized compensation cost related to unvested stock-based compensation grants | $				$ 1,700,000			$ 1,700,000
Weighted-average remaining recognition period							2 years 2 months 12 days
Stock-based compensation | $							$ 998,000	$ 1,177,000
Number of warrant to purchase common stock issued				2,826,687			2,826,687
Warrants issued, exercise price | $ / shares			$ 330.40	$ 18.78			$ 18.78
June Purchase Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award and Warrants [Line Items]
Number of warrant to purchase common stock issued				1,282,832			1,282,832
Warrants issued, exercise price | $ / shares				$ 10.7258			$ 10.7258
Series D Redeemable Convertible Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award and Warrants [Line Items]
Warrants issued, exercise price | $ / shares						$ 363.20
Warrant, exercisable term						5 years
Warrant issued, shares of common stock called by warrant						61,397
Series D Redeemable Convertible Preferred Stock [Member] | Placement Agent [Member]
Share-based Compensation Arrangement by Share-based Payment Award and Warrants [Line Items]
Warrants issued, exercise price | $ / shares						$ 268.80
Warrant issued, shares of common stock called by warrant						1,674
Mahyco International [Member]
Share-based Compensation Arrangement by Share-based Payment Award and Warrants [Line Items]
Warrant issued, shares of common stock called by warrant			3,784
Warrant, exercisable term			5 years
2015 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award and Warrants [Line Items]
Total number of shares reserved for issuance under plan				89,489			89,489
Percentage in payroll deductions to acquire shares of common stock		15.00%
Purchase plan offering period		6 months
Employees are able to purchase company's common stock on first trading day of offering period, percentage		85.00%
Issuance of common stock pursuant to employee stock purchase plan							6,853
Stock-based compensation | $				$ 4,000	$ 6,000		$ 6,000	$ 11,000
Private Placement [Member] | June Purchase Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award and Warrants [Line Items]
Number of warrant to purchase common stock issued				1,461,962			1,461,962
Private Placement [Member] | June Purchase Agreement [Member] | Purchase Price Of 94 [Member]
Share-based Compensation Arrangement by Share-based Payment Award and Warrants [Line Items]
Number of warrant to purchase common stock issued				1,392,345			1,392,345
Warrants issued, purchase price of warrants per share | $ / shares				$ 9.94			$ 9.94
Private Placement [Member] | June Purchase Agreement [Member] | Exercise Price Of 12568 [Member]
Share-based Compensation Arrangement by Share-based Payment Award and Warrants [Line Items]
Number of warrant to purchase common stock issued				69,617			69,617
Warrants issued, exercise price | $ / shares				$ 12.568			$ 12.568
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award and Warrants [Line Items]
Warrants issued, exercise price | $ / shares				$ 8.322			$ 8.322
2015 Omnibus Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award and Warrants [Line Items]
Terms under the plan							The 2015 Plan became effective in May 2015 and all shares that were reserved, but not issued, under the 2006 Plan were assumed by the 2015 Plan. Upon effectiveness, the 2015 Plan had 154,387 shares of common stock reserved for future issuance, which included 10,637 shares under the 2006 Plan that were transferred to and assumed by the 2015 Plan. The 2015 Plan provides for automatic annual increases in shares available for grant. In addition, shares subject to awards under the 2006 Plan that are forfeited or canceled will be added to the 2015 Plan.
Total number of shares reserved for issuance under plan	154,387			484,539			484,539
Options vesting period	4 years			2 years
Common stock available for future grant				26,740			26,740
Total number of options outstanding				457,797			457,797
2015 Omnibus Equity Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award and Warrants [Line Items]
Options exercisable period	10 years
2015 Omnibus Equity Incentive Plan [Member] | Share-based Compensation Award, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award and Warrants [Line Items]
Stock options vesting percentage at end of one year	25.00%
2006 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award and Warrants [Line Items]
Total number of shares reserved for issuance under plan	10,637
Total number of options outstanding				67,397			67,397