Warrants - Additional Information (Detail) $ / shares in Units, $ in Millions								12 Months Ended
	Sep. 12, 2017 USD ($) $ / shares shares	May 10, 2017 $ / shares shares	Apr. 28, 2017 $ / shares shares	Aug. 14, 2015 $ / shares shares	Sep. 26, 2014 $ / shares shares	Mar. 22, 2013 USD ($) Investor $ / shares shares	Jan. 17, 2012 $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2013 shares	Sep. 03, 2013 shares
Class of Warrant or Right [Line Items]
Offering price | $ / shares			$ 1.00
Warrants to purchase common shares			24,900,000
Warrants outstanding												1,200,000
Warrants exercised			0
Warrants Not Settleable in Cash [Member]
Class of Warrant or Right [Line Items]
Share-based compensation arrangement by share-based payment award, Equity instruments other than options, aggregate intrinsic value, outstanding | $								$ 5.3	$ 11.2	$ 0.0
Minimum [Member]
Class of Warrant or Right [Line Items]
Percentage of warrants exercisability limitation percentage								4.99%
Outstanding voting stock acquisition minimum threshold percentage to assume warrant obligations								50.00%
Series A Warrant [Member]
Class of Warrant or Right [Line Items]
Warrants, exercise price | $ / shares			$ 1.00
Warrant expiration date			Oct. 31, 2017
Series B Warrant [Member]
Class of Warrant or Right [Line Items]
Warrants, exercise price | $ / shares			$ 1.00					$ 1.00
Warrants exercised								8,893,700	7,052,215
Service Warrants [Member] | Service Agreement [Member]
Class of Warrant or Right [Line Items]
Warrants, exercise price | $ / shares	$ 1.00
Warrant, expiration period	10 years
Warrants exercised								650,000	0
Common stock warrants issued	950,000
Percentage of vesting date of execution agreement	25.00%
Percentage of vesting completion of hiring the sales term	50.00%
Percentage of vesting achieving cumulative product revenue	25.00%
Achieving cumulative product revenue | $	$ 15.0
Recognized initial expense | $									$ 0.6
Common Stock [Member]
Class of Warrant or Right [Line Items]
Number of common stock or warrants in each unit			1
Common Stock [Member] | Series A Warrant [Member]
Class of Warrant or Right [Line Items]
Warrants, exercise price | $ / shares			$ 1.00
Number of common stock or warrants in each unit			1
Common Stock [Member] | Series B Warrant [Member]
Class of Warrant or Right [Line Items]
Warrants, exercise price | $ / shares			$ 1.00
Number of common stock or warrants in each unit			0.75
First Amended SVB Loan Agreement [Member]
Class of Warrant or Right [Line Items]
Warrants, exercise price | $ / shares					$ 4.015
Warrant, expiration period					7 years
Warrants exercised								27,880	0	0
Stock issued due to exercise of options								8,580
Common stock warrants issued					38,324
Second Amended SVB Loan Agreement [Member]
Class of Warrant or Right [Line Items]
Warrants, exercise price | $ / shares				$ 3.10
Warrant, expiration period				7 years
Warrants exercised								67,742	0	0
Stock issued due to exercise of options								31,535
Common stock warrants issued				112,903
Stock Purchase Agreement 2013 [Member] | 2013 PIPE investors [Member]
Class of Warrant or Right [Line Items]
Number of investors | Investor						17
Stock issued, shares						2,420,000
Offering price | $ / shares						$ 1.25
Proceeds from PIPE | $						$ 3.0
Warrants to purchase common shares						1,209,600
Warrants, exercise price | $ / shares						$ 1.65
Warrant, expiration period						5 years
Merger Agreement [Member]
Class of Warrant or Right [Line Items]
Exchange ratio												1.1533
Loan and Security Agreement [Member] | Term Loan [Member]
Class of Warrant or Right [Line Items]
Warrant, expiration period		5 years
Warrants exercised								0
Loan and Security Agreement [Member] | Term Loan [Member] | First Tranche [Member]
Class of Warrant or Right [Line Items]
Warrants, exercise price | $ / shares		$ 1.00
Loan and Security Agreement [Member] | Maximum [Member] | Term Loan [Member] | First Tranche [Member]
Class of Warrant or Right [Line Items]
Warrants to purchase common shares		1,244,746
Related Parties [Member] | Stock Purchase Agreement 2013 [Member] | 2013 PIPE investors [Member]
Class of Warrant or Right [Line Items]
Stock issued, shares						1,280,000
Warrants to purchase common shares						640,000
Warrants exercised								800,000	240,000	0
Prior Lenders [Member]
Class of Warrant or Right [Line Items]
Warrants to purchase common shares							279,588
Warrants, exercise price | $ / shares							$ 1.45
Warrant, expiration period							10 years
Warrants exercised								139,794	0	0	139,794
Stock issued due to exercise of options								104,845			112,766