Warrants (Tables)

3 Months Ended

Mar. 31, 2019

Warrants and Rights Note Disclosure [Abstract]

Schedule of Warrant Activity

	Common Stock Warrants		Weighted Average Exercise Price
Outstanding at January 1, 2019		1,710,609	$	7.33
Issued		—		—
Expired		—		—
Outstanding at March 31, 2019		1,710,609	$	7.33

Schedule of Warrant Valuation Assumptions

The estimated fair value was derived using a valuation model with the following weighted-average assumptions:

	Three Months Ended March 31,
	2019			2018
Value of underlying common stock (per share)	$	3.05		$	7.89
Risk free interest rate		2.3	%		2.3	%
Expected term in years		3.5			4.3
Volatility		93	%		98	%
Dividend yield		0	%		0	%

Schedule of Warrants Activities Used in Derivative Liability

The following table summarizes our activities related to warrants accounted for as a derivative liability for the three months ended March 31, 2019 and 2018:

	2019		2018
Balance at January 1,		87,509		93,759
Derivative warrants issued		—		—
Derivative warrants exercised		—		—
Derivative warrants expired		—		—
Balance at March 31,		87,509		93,759