Stock-Based Compensation - Additional Information (Detail)			3 Months Ended		6 Months Ended
	May 20, 2015 shares	May 14, 2015	Jun. 30, 2016 USD ($) $ / shares shares	Jun. 30, 2015 $ / shares	Jun. 30, 2016 USD ($) IncentivePlan $ / shares shares	Jun. 30, 2015 USD ($) $ / shares	Dec. 31, 2015 shares	Jun. 30, 2014 $ / shares shares	Dec. 31, 2013 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity incentive plans | IncentivePlan					2
Total number of options outstanding			3,768,293		3,768,293		3,427,509
Unrecognized compensation cost related to unvested stock-based compensation grants | $			$ 880,000		$ 880,000
Weighted-average remaining recognition period					2 years 10 months 13 days
Weighted-average estimated grant-date fair value of stock options granted | $ / shares			$ 0.72	$ 5.35	$ 0.72	$ 1.28
Stock-based compensation | $					$ 393,000	$ 924,000
Warrant, exercisable term					5 years
Placement Agent [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock warrants, exercise price per share | $ / shares								$ 13.45
Common stock warrants issued								33,445
Series D Redeemable Convertible Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock warrants, exercise price per share | $ / shares								$ 18.16
Common stock warrants issued								1,227,783
Mahyco Convertible Promissory Notes [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of warrant to purchase common stock issued			75,666		75,666				75,666
Common stock warrants, exercise price per share | $ / shares			$ 16.52		$ 16.52				$ 16.52
Warrant, exercisable term					5 years
2015 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of shares reserved for issuance under plan			1,027,741		1,027,741
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					34,759
First offering period, start date		May 14, 2015
First offering period, end date		Feb. 01, 2016
Stock-based compensation | $			$ 26,000		$ 56,000
2006 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of shares reserved for issuance under plan	212,729
Total number of options outstanding			2,973,293		2,973,293
2015 Omnibus Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options vesting period	4 years
Terms under the plan					The 2015 Plan became effective upon the IPO 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 3,087,729 shares of common stock reserved for future issuance, which included 212,729 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, beginning on January 1, 2016. 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	3,087,729		5,036,426		5,036,426
Common stock available for future grant			4,241,426		4,241,426
Total number of options outstanding			795,000		795,000
2015 Omnibus Equity Incentive Plan [Member] | Share-based Compensation Award, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting percentage at end of one year	25.00%
Minimum [Member] | Unvested Options [Member] | 2006 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options vesting period					2 years 3 months
Maximum [Member] | 2015 Omnibus Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options exercisable period	10 years
Maximum [Member] | Unvested Options [Member] | 2006 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options vesting period					4 years