Embedded Derivatives - Additional Information (Detail) - USD ($)	1 Months Ended					9 Months Ended
	May. 31, 2015	Feb. 28, 2015	Aug. 31, 2014	Dec. 31, 2013	Jul. 31, 2012	Sep. 30, 2015	Dec. 31, 2014
Derivative [Line Items]
Additional purchase of common stock shares						7,283,584
Derivative warrant liability fair value						$ 3,395,000	$ 3,114,000
Proceeds from the exercise of warrants						$ 10,150,863
2013 Warrants
Derivative [Line Items]
Common Stock Units Issued				1,420,250
Additional purchase of common stock shares				1,420,250		1,420,250
Warrants expiration date						Dec. 16, 2018
Warrant , Exercise Price	$ 15.30					$ 12.65
Cash inducement fee for each share of common stock	11.55
Net proceeds from warrants exercises, per share	3.75
Proceeds from the exercise of warrants						$ 1,057,010
2014 Warrants
Derivative [Line Items]
Common Stock Units Issued			2,000,000
Additional purchase of common stock shares			1,000,000			1,000,000
Warrants expiration date						Aug. 05, 2019
Warrant , Exercise Price	9.60					$ 8.30
Cash inducement fee for each share of common stock	5.85
Net proceeds from warrants exercises, per share	$ 3.75
Proceeds from the exercise of warrants						$ 2,204,540
2015 Warrants
Derivative [Line Items]
Common Stock Units Issued	4,300,000	2,216,667
2015 Warrants | Series A
Derivative [Line Items]
Additional purchase of common stock shares		2,216,667				2,216,667
Warrants expiration date						Feb. 03, 2020
Warrant , Exercise Price						$ 3.75
Proceeds from the exercise of warrants						$ 1,302,750
2015 Warrants | Series B
Derivative [Line Items]
Additional purchase of common stock shares		2,216,667				2,216,667
Adjusted market price of shares						less than $3.00
Warrants expiration date						Aug. 03, 2015
Warrant , Exercise Price						$ 3.00
Proceeds from the exercise of warrants						$ 5,586,564
2015 Warrants | Series C
Derivative [Line Items]
Additional purchase of common stock shares	430,000					430,000
Warrants expiration date						May 19, 2020
Warrant , Exercise Price						$ 5.50
2013 and 2014 Warrants
Derivative [Line Items]
Proceeds from the exercise of warrants	$ 3,430,000
2022 Notes
Derivative [Line Items]
Percentage of convertible senior notes embedded derivatives					7.50%
7.5% convertible senior notes, maturity date					2022
2022 notes, conversion date					Jul. 01, 2017	Jul. 01, 2017