Schedule of Shares Issued Upon Exercise of Warrants (Detail) - $ / shares	1 Months Ended								3 Months Ended
	Feb. 28, 2017	Sep. 30, 2016	Apr. 30, 2016	Dec. 31, 2015	May 31, 2015	Feb. 28, 2015	Aug. 31, 2014	Dec. 31, 2013	Mar. 31, 2017
Derivative [Line Items]
Additional purchase of common stock shares									17,106,683
Shares Issued upon Warrant Exercises									(2,946,422)
Shares Underlying Warrants Outstanding									14,017,373
Series A
Derivative [Line Items]
Warrant, Issuance Date									Feb. 03, 2015
Warrants, Expiration date									Feb. 03, 2020
Warrant , Exercise Price									$ 1.90
Additional purchase of common stock shares						110,833			110,833
Shares Issued upon Warrant Exercises									(99,416)
Shares Underlying Warrants Outstanding									11,417
Series B
Derivative [Line Items]
Warrant, Issuance Date									Feb. 03, 2015
Warrants, Expiration date									Aug. 03, 2015
Additional purchase of common stock shares						110,883			110,833
Shares Issued upon Warrant Exercises									(96,795)
Series C
Derivative [Line Items]
Warrant, Issuance Date									May 19, 2015
Warrants, Expiration date									May 19, 2020
Warrant , Exercise Price									$ 9.59
Additional purchase of common stock shares					21,500				21,500
Shares Underlying Warrants Outstanding									21,500
Series D
Derivative [Line Items]
Warrant, Issuance Date									Dec. 11, 2015
Warrants, Expiration date									Dec. 11, 2020
Warrant , Exercise Price									$ 2.00
Additional purchase of common stock shares				502,500					502,500
Shares Issued upon Warrant Exercises									(501,570)
Shares Underlying Warrants Outstanding									930
Series E
Derivative [Line Items]
Warrant, Issuance Date									Dec. 11, 2015
Warrants, Expiration date									Dec. 11, 2016
Additional purchase of common stock shares				400,000					400,000
Shares Issued upon Warrant Exercises									(400,000)
Series F
Derivative [Line Items]
Warrant, Issuance Date									Apr. 01, 2016
Warrants, Expiration date									Apr. 01, 2021
Warrant , Exercise Price									$ 2.00
Additional purchase of common stock shares			514,644						514,644
Shares Issued upon Warrant Exercises									(233,857)
Shares Underlying Warrants Outstanding									280,787
Series J
Derivative [Line Items]
Warrant, Issuance Date									Sep. 13, 2016
Warrants, Expiration date									Sep. 13, 2017
Additional purchase of common stock shares		185,000							185,000
Shares Issued upon Warrant Exercises									(185,000)
Series G
Derivative [Line Items]
Warrant, Issuance Date									Apr. 01, 2016
Warrants, Expiration date									Apr. 01, 2017
Additional purchase of common stock shares			328,571						328,571
Shares Issued upon Warrant Exercises									(328,571)
Series H
Derivative [Line Items]
Warrant, Issuance Date									Apr. 01, 2016
Warrants, Expiration date									Oct. 01, 2016
Additional purchase of common stock shares			1,029,286						1,029,286
Shares Issued upon Warrant Exercises									(900,436)
Series I
Derivative [Line Items]
Warrant, Issuance Date									Sep. 13, 2016
Warrants, Expiration date									Sep. 13, 2021
Warrant , Exercise Price									$ 11.00
Additional purchase of common stock shares		712,503							712,503
Shares Underlying Warrants Outstanding									712,503
Series K
Derivative [Line Items]
Warrant, Issuance Date									Feb. 17, 2017
Warrants, Expiration date									Feb. 17, 2022
Warrant , Exercise Price									$ 2.35
Additional purchase of common stock shares	6,250,000								6,250,000
Shares Underlying Warrants Outstanding									6,250,000
Series L
Derivative [Line Items]
Warrant, Issuance Date									Feb. 17, 2017
Warrants, Expiration date									Feb. 17, 2018
Warrant , Exercise Price									$ 0.01
Additional purchase of common stock shares	570,000								570,000
Shares Issued upon Warrant Exercises									(155,000)
Shares Underlying Warrants Outstanding									415,000
Series M
Derivative [Line Items]
Warrant, Issuance Date									Feb. 17, 2017
Warrants, Expiration date									Nov. 17, 2017
Warrant , Exercise Price									$ 2.35
Additional purchase of common stock shares	6,250,000								6,250,000
Shares Underlying Warrants Outstanding									6,250,000
2013 Warrants
Derivative [Line Items]
Warrant, Issuance Date									Dec. 16, 2013
Warrants, Expiration date									Dec. 16, 2018
Warrant , Exercise Price									$ 15.84
Additional purchase of common stock shares								71,013	71,013
Shares Issued upon Warrant Exercises									(15,239)
Shares Underlying Warrants Outstanding									55,774
2014 Warrants
Derivative [Line Items]
Warrant, Issuance Date									Aug. 05, 2014
Warrants, Expiration date									Aug. 05, 2019
Warrant , Exercise Price									$ 11.98
Additional purchase of common stock shares							50,000		50,000
Shares Issued upon Warrant Exercises									(30,538)
Shares Underlying Warrants Outstanding									19,462