Quarterly report pursuant to Section 13 or 15(d)

Stock Warrants - Schedule of Warrants Outstanding (Detail)

Stock Warrants - Schedule of Warrants Outstanding (Detail) - $ / shares	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Jun. 12, 2015	Aug. 01, 2014
Class of Warrant or Right [Line Items]
Shares Underlying Outstanding Warrants	31,265,182	36,270,103
Weighted-average exercise price per share	$ 2.31	$ 2.74
Placement Agent Warrants [Member]
Class of Warrant or Right [Line Items]
Shares Underlying Outstanding Warrants	189,126	189,126
Representative's Warrant [Member]
Class of Warrant or Right [Line Items]
Exercise Prices	$ 7.50
Shares Underlying Outstanding Warrants	206,410	206,410
Other Warrants [Member]
Class of Warrant or Right [Line Items]
Shares Underlying Outstanding Warrants	180,338	194,623
Exercise Price Less Than or Equal to $2.00 [Member]
Class of Warrant or Right [Line Items]
Shares Underlying Outstanding Warrants	16,002,164
Expiration Start Date	Sep. 01, 2021
Expiration End Date	Jul. 25, 2022
Exercise Price $2.01 - $4.99 [Member]
Class of Warrant or Right [Line Items]
Shares Underlying Outstanding Warrants	14,983,085
Expiration Start Date	Oct. 28, 2018
Expiration End Date	Jul. 27, 2021
Exercise Price Greater Than or Equal to $ 5.00 [Member]
Class of Warrant or Right [Line Items]
Shares Underlying Outstanding Warrants	279,933
Expiration Start Date	Jul. 22, 2019
Expiration End Date	Jan. 05, 2022
Minimum [Member] \| Exercise Price $2.01 - $4.99 [Member]
Class of Warrant or Right [Line Items]
Exercise Prices	$ 2.01
Minimum [Member] \| Exercise Price Greater Than or Equal to $ 5.00 [Member]
Class of Warrant or Right [Line Items]
Exercise Prices	5.00
Maximum [Member] \| Exercise Price Less Than or Equal to $2.00 [Member]
Class of Warrant or Right [Line Items]
Exercise Prices	2.00
Maximum [Member] \| Exercise Price $2.01 - $4.99 [Member]
Class of Warrant or Right [Line Items]
Exercise Prices	$ 4.99
Note Warrants [Member]
Class of Warrant or Right [Line Items]
Exercise Prices				$ 3.00
Shares Underlying Outstanding Warrants	692,858	3,315,878		3,321,416
Private Placement [Member]
Class of Warrant or Right [Line Items]
Exercise Prices	$ 4.65		$ 8.00
Warrants [Member] \| Private Placement [Member]
Class of Warrant or Right [Line Items]
Shares Underlying Outstanding Warrants		2,364,066
2016 Warrants [Member]
Class of Warrant or Right [Line Items]
Shares Underlying Outstanding Warrants	14,000,000	14,000,000
2017 Warrants [Member]
Class of Warrant or Right [Line Items]
Shares Underlying Outstanding Warrants	15,996,450	16,000,000