Stock Plans - Additional Information (Detail)		1 Months Ended		12 Months Ended
	Aug. 28, 2014 $ / shares shares	Jan. 31, 2017 shares	Aug. 31, 2014 USD ($)	Dec. 31, 2016 USD ($) Milestone $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014	Jan. 01, 2017 shares
Stockholders Equity [Line Items]
Common stock withheld pursuant to employee stock purchase plan | $				$ 155,000	$ 63,000
Subsequent Event [Member] | Restricted Stock Units [Member]
Stockholders Equity [Line Items]
Number of shares granted by board | shares		916,000
Vesting period		4 years
2004 Stock Option Plan [Member]
Stockholders Equity [Line Items]
Stock-based compensation expense | $				0	0
Unrecognized compensation cost related to non-vested stock options | $				0
Stock options, intrinsic value | $				0
2014 Stock Option and Incentive Plan [Member]
Stockholders Equity [Line Items]
Stock-based compensation expense | $				2,843,000	$ 1,389,000
Unrecognized compensation cost related to non-vested stock options | $				7,692,000
Stock options, intrinsic value | $				$ 2,064,000
Number of shares reserved for future issuance | shares				3,034
Percentage of outstanding common stock increased to shares available for grant				4.00%
Stock options granted | shares	840,975			1,156,500	730,500
Expiration period of stock options	10 years			10 years	10 years
Stock options, dividend yield				0.00%	0.00%	0.00%
Weighted Average Exercise Price Per Share, Granted | $ / shares	$ 4.342			$ 7.77	$ 5.69
Stock options, terms of vesting				These stock options vested 25% on the one-year anniversary of the grant date and the remaining 75% will vest in equal monthly installments over the following 36 months.
Weighted-average fair value of stock option granted | $ / shares				$ 5.23	4.39
Closing price of common stock | $ / shares				$ 6.10	$ 11.33
Total options exercised | shares				84,428	9,857
Number of shares surrendered pursuant to net exercise right | shares				30,118
2014 Stock Option and Incentive Plan [Member] | Restricted Stock Units [Member]
Stockholders Equity [Line Items]
Stock-based compensation expense | $				$ 0
Stock options, terms of vesting				Vesting for these RSU’s was based equally on the achievement of two performance-based conditions, subject to continued service through such achievement dates.
Number of common stock received for contingent right | shares				1
Number of vesting achievement of performance-based conditions | Milestone				2
Intrinsic fair value, date of grant | $				$ 3,055
Number of shares outstanding | shares				470,000
Aggregate number of outstanding shares | shares				3,134,832
2014 Stock Option and Incentive Plan [Member] | Restricted Stock Units [Member] | Executive Officers [Member]
Stockholders Equity [Line Items]
Number of shares granted by board | shares				470,000
2014 Stock Option and Incentive Plan [Member] | Share-based Compensation Award, Tranche One [Member]
Stockholders Equity [Line Items]
Stock-based compensation expense | $			$ 2,798,000	$ 5,950,000	$ 3,209,000
Stock options, vesting percentage	25.00%
2014 Stock Option and Incentive Plan [Member] | Vest Equally Over 36 Months [Member]
Stockholders Equity [Line Items]
Stock options, vesting percentage	75.00%
2014 Stock Option and Incentive Plan [Member] | Minimum [Member]
Stockholders Equity [Line Items]
Stock options, expected term				5 years 3 months 22 days	5 years 3 months 22 days	5 years
Stock options, expected stock price volatility				76.90%	80.90%	83.30%
Stock options, risk free rate				1.20%	1.55%	1.63%
2014 Stock Option and Incentive Plan [Member] | Maximum [Member]
Stockholders Equity [Line Items]
Stock options, expected term				6 years 29 days	6 years 29 days	6 years 3 months
Stock options, expected stock price volatility				82.40%	101.10%	92.50%
Stock options, risk free rate				2.08%	1.85%	1.84%
2014 Stock Option and Incentive Plan [Member] | General and Administrative Expense [Member]
Stockholders Equity [Line Items]
Stock-based compensation expense | $				$ 1,521,000	$ 795,000
2014 Stock Option and Incentive Plan [Member] | Research and Development Expense [Member]
Stockholders Equity [Line Items]
Stock-based compensation expense | $				1,322,000	594,000
2014 Stock Option and Incentive Plan [Member] | Subsequent Event [Member]
Stockholders Equity [Line Items]
Number of shares reserved for future issuance | shares							1,079,453
Employee Stock Purchase Plan [Member]
Stockholders Equity [Line Items]
Stock-based compensation expense | $				$ 66,000	41,000
Number of shares reserved for future issuance | shares				600,000
Percentage of outstanding common stock increased to shares available for grant				1.00%
Number of shares available for issuance | shares				238,308
Percentage of minimum voting power of common stock not eligible to purchase shares				5.00%
Maximum payroll deduction of employee compensation, percentage				10.00%
Discount rate employees purchase shares on offering period				85.00%
Maximum number of shares purchased by an employee | shares				5,000
Maximum worth of stock an employee purchases | $				$ 25,000,000
Common stock withheld pursuant to employee stock purchase plan | $				$ 155,000	$ 63,000
Number of shares issued | shares				25,925	13,143
Employee Stock Purchase Plan [Member] | Subsequent Event [Member]
Stockholders Equity [Line Items]
Number of shares reserved for future issuance | shares							31,555