Warrants - (Tables)

12 Months Ended

Dec. 31, 2018

Equity [Abstract]

Outstanding Liability Classified Warrants to Purchase Common Stock

The following table summarizes the Company’s outstanding warrants to purchase common stock as of:

	Number of Warrants
	December 31, 2018	December 31, 2017	Exercise  Price		Expiration Dates
Liability-classified Warrants
Issued with June 2012 Convertible Notes	—	75,040	$	37.50	Jun 2018
Issued in Series E Preferred Stock offering	—	104,676	$	112.50	Dec 2018
Issued with September 2016 Convertible Notes	1,205,840	1,205,840	$	22.50	Sept 2021
	1,205,840	1,385,556
Equity-classified Warrants
Issued in 2017 Series A Preferred Stock Offering	687,468	687,468	$	12.69	Mar 2022
Issued in 2017 Common Stock Offering - common warrants	2,679,702	2,809,404	$	3.85	Dec 2022
Issued in 2017 Common Stock Offering - underwriter warrants	87,274	87,274	$	4.8125	Dec 2022
Issued in 2017 Common Stock Offering - pre-funded warrants	—	483,221	$	0.05	No expiration
Issued in May 2018 Private Placement - common warrants	1,528,668	—	$	2.86	Nov 2023
Issued in May 2018 Registered Direct Offering - underwriter warrants	142,676	—	$	3.679	May 2023
Issued in July 2018 Private Placement - common warrants	958,152	—	$	2.70	Jan 2024
Issued in July 2018 Registered Direct Offering - underwriter warrants	103,186	—	$	3.464	Jul 2023
	6,187,126	4,067,367
Total outstanding warrants	7,392,966	5,452,923

Summary of Warrant Activity

The table below is a summary of the Company’s warrant activity for the year ended December 31, 2018.

	Number of warrants
	Liability-classified		Equity-classified		Total		Weighted-average exercise price
Outstanding at December 31, 2017	1,385,556		4,067,367		5,452,923		$	11.32
Granted	—		2,732,682		2,732,682		2.87
Exercised	—		(612,923	)	(612,923	)	0.85
Expired	(179,716	)	—		(179,716	)	81.18
Outstanding at December 31, 2018	1,205,840		6,187,126		7,392,966		$	7.36

Calculated Aggregate Fair Values and Net Cash Settlement Value

The following table summarizes the calculated aggregate fair values, along with the assumptions utilized in each calculation: 

($ in thousands, except per share data)	December 31, 2018			December 31, 2017
Calculated aggregate value	$	152		$	1,073
Weighted average exercise price per share	$	22.50		$	30.10
Closing price per share of common stock	$	1.50		$	3.20
Volatility	94.1		%	92.2		%
Weighted average remaining expected life	2 years, 8 months			3 years, 4 months
Risk-free interest rate	2.45		%	2.00		%
Dividend yield	—			—