Related-Party Transactions (Tables)

9 Months Ended

Sep. 30, 2019

Certain terms of these Letter Agreements are set forth in the table below:

	December 5, 2017 Letter Agreement		July 30, 2018 Letter Agreement		December 11, 2018 Letter Agreement		March 18, 2019 Letter Agreement		September 26, 2019 Letter Agreement
Aggregate dollar value to be sold under agreement	$10.0 million		$10.0 million		$10.0 million		$9.0 million		$10.0 million
Specified purchase price per share	$	4.38	$	1.33	$	1.84	$	1.65	$	1.46
Expiration date of letter agreement	December 5, 2018		July 30, 2019		December 11, 2019		March 18, 2020		September 26, 2020
Shares available to be issued under related warrants		198,267		518,654		340,534		—		400,990
Exercise price of related warrants	$	5.04	$	1.53	$	2.12	$	—	$	1.68
Expiration date of related warrants	December 5, 2024		July 30, 2025		December 11, 2025				September 26, 2026
Total shares issued as of September 30, 2019		2,283,105		7,518,797		5,434,783		5,454,546		1,369,863
Remaining shares to be issued as of September 30, 2019		—		—		—		—		5,479,453

Assumptions Used to Calculate Fair Value of Warrants

Significant inputs utilized in the valuation of the Letter Agreement Warrants as of September 30, 2019 were:

	September 30, 2019	December 31, 2018
Expected volatility	110.41% - 120.54%	108.53% - 115.04%
Risk-free interest rate	1.56% - 1.66%	2.59% - 2.69%

Warrant Liability [Member]

Assumptions Used to Calculate Fair Value of Warrants

Fair value of the Letter Agreement Warrants issued during the three and nine months ended September 30, 2019 and 2018 was calculated as of their issuance date using the methods described in Note 13 using the following assumptions:

	July 30, 2018		September 26, 2019
Expected volatility	95.29%		110.35%
Expected life of option, in years		7.0		7.0
Risk-free interest rate	2.94%		1.65%
Expected dividend yield	0.00%		0.00%