Warrants to Purchase Shares of Common Stock Outstanding (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2016	Aug. 31, 2014
Class Of Warrant Or Right [Line Items]
Warrants, Outstanding	1,103,766
Series A
Class Of Warrant Or Right [Line Items]
Warrant, Issuance Date	Feb. 03, 2015
Warrants, Expiration Date	Feb. 03, 2020
Warrants, Outstanding	11,417
Warrant , Exercise Price	$ 5.80
Series C
Class Of Warrant Or Right [Line Items]
Warrant, Issuance Date	May 19, 2015
Warrants, Expiration Date	May 19, 2020
Warrants, Outstanding	21,500
Warrant , Exercise Price	$ 27.80
Series D
Class Of Warrant Or Right [Line Items]
Warrant, Issuance Date	Dec. 11, 2015
Warrants, Expiration Date	Dec. 11, 2020
Warrants, Outstanding	930
Warrant , Exercise Price	$ 2.00
Series E
Class Of Warrant Or Right [Line Items]
Warrant, Issuance Date	Dec. 11, 2015
Warrants, Expiration Date	Dec. 31, 2016
Series F
Class Of Warrant Or Right [Line Items]
Warrant, Issuance Date	Apr. 01, 2016
Warrants, Expiration Date	Apr. 01, 2021
Warrants, Outstanding	280,787
Warrant , Exercise Price	$ 5.80
Series G
Class Of Warrant Or Right [Line Items]
Warrant, Issuance Date	Apr. 01, 2016
Warrants, Expiration Date	Apr. 01, 2017
Series H
Class Of Warrant Or Right [Line Items]
Warrant, Issuance Date	Apr. 01, 2016
Warrants, Expiration Date	Oct. 01, 2016
Series I
Class Of Warrant Or Right [Line Items]
Warrant, Issuance Date	Sep. 13, 2016
Warrants, Expiration Date	Sep. 13, 2021
Warrants, Outstanding	712,503
Warrant , Exercise Price	$ 11.00
Series J
Class Of Warrant Or Right [Line Items]
Warrant, Issuance Date	Sep. 13, 2016
Warrants, Expiration Date	Sep. 13, 2017
2013 Warrants
Class Of Warrant Or Right [Line Items]
Warrant, Issuance Date	Dec. 16, 2013
Warrants, Expiration Date	Dec. 16, 2018
Warrants, Outstanding	55,774
Warrant , Exercise Price	$ 49.80
2014 Warrants
Class Of Warrant Or Right [Line Items]
Warrant, Issuance Date	Aug. 05, 2014
Warrants, Expiration Date	Aug. 05, 2019
Warrants, Outstanding	19,462
Warrant , Exercise Price	$ 36.20	$ 36.20
TriplePoint Capital LLC | Warrant 1
Class Of Warrant Or Right [Line Items]
Warrant, Issuance Date	Aug. 31, 2010
Warrants, Expiration Date	Aug. 31, 2017
Warrants, Outstanding	666
Warrant , Exercise Price	$ 17.70
TriplePoint Capital LLC | Warrant 2
Class Of Warrant Or Right [Line Items]
Warrant, Issuance Date	Oct. 31, 2011
Warrants, Expiration Date	Oct. 31, 2018
Warrants, Outstanding	523
Warrant , Exercise Price	$ 17.70
TriplePoint Capital LLC | Warrant 3
Class Of Warrant Or Right [Line Items]
Warrant, Issuance Date	Jan. 31, 2012
Warrants, Expiration Date	Oct. 31, 2018
Warrants, Outstanding	104
Warrant , Exercise Price	$ 17.70
Genesis Select
Class Of Warrant Or Right [Line Items]
Warrant, Issuance Date	Jun. 30, 2013
Warrants, Expiration Date	Jun. 30, 2018
Warrants, Outstanding	100
Warrant , Exercise Price	$ 24.45