The Company and Basis of Presentation - Additional Information (Detail) $ / shares in Units, $ in Millions				9 Months Ended	12 Months Ended
	Jul. 21, 2015 $ / shares shares	Jul. 15, 2015 USD ($) $ / shares shares	Jun. 29, 2015	Sep. 30, 2016 USD ($) $ / shares shares	Dec. 31, 2015 $ / shares shares
Class of Stock [Line Items]
Shares issued, price per share | $ / shares	$ 17.00
Convertible preferred stock, conversion basis				On July 21, 2015, immediately prior to the closing of the IPO, all outstanding shares of convertible and redeemable convertible preferred stock converted into 18,361,953 shares of common stock, including an aggregate of 390,680 shares of common stock that were issued pursuant to the net exercise of 493,648 preferred stock warrants at the IPO price of $17.00 per share and an aggregate of 481,671 shares of common stock that were issued pursuant to the cash exercise of 481,671 preferred stock warrants. The IPO closed on July 21, 2015.
Number of common stock shares issued upon exercise of preferred stock warrants	390,680				481,671
Preferred stock warrants exercised	493,648
Capital stock, authorized	510,000,000
Common stock, shares authorized	500,000,000			500,000,000	500,000,000
Preferred stock, shares authorized	10,000,000			10,000,000	10,000,000
Preferred stock, par value | $ / shares	$ 0.001			$ 0.001	$ 0.001
Common stock, par value | $ / shares	$ 0.001			$ 0.001	$ 0.001
Reverse stock split, description				7.45-to-1
Reverse Stock Split, Conversion Ratio			0.13422818
Reverse stock split, effective date				Jul. 02, 2015
Series B and B-1 Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Cumulative dividends | $				$ 5.5
Series C and D Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Issuable common stock to redeemable convertible preferred stockholders				750,946	750,946
Common Stock [Member]
Class of Stock [Line Items]
Stock issued, shares					9,315,000
Redeemable convertible preferred stock converted into common stock	18,361,953
Common Stock [Member] | Series C and D Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Issuable common stock to redeemable convertible preferred stockholders					750,946
Cash Exercise [Member]
Class of Stock [Line Items]
Number of common stock shares issued upon exercise of preferred stock warrants	481,671
Preferred stock warrants exercised	481,671
Initial Public Offering [Member]
Class of Stock [Line Items]
Stock issued, shares		9,315,000
Shares issued, price per share | $ / shares		$ 17.00
Proceeds from issuance of common stock, net of deferred financing costs | $		$ 143.6