Purchase Agreement, Controlled Equity Offering and Public Offering of Common Stock (Tables)

12 Months Ended

Dec. 31, 2018

Purchase Agreement Controlled Equity Offering And Public Offering Of Common Stock [Abstract]

Schedule of Amounts Offered and Sold under 2015, 2016 and 2017 Sales Agreement

The amounts offered and sold under the 2015 Sales Agreement, 2016 Sales Agreement and the 2017 Sales Agreement are as set forth below (in thousands, except per share amounts):

	2017 Sales Agreement		2016 Sales Agreement		2015 Sales Agreement
	Year Ended December 31, 2017		Year  Ended December 31, 2016		Year Ended December 31, 2016		Year Ended December 31, 2015
Total shares of common stock sold		15,998.5		8,763.4		5,710.2		2,014.3
Average price per share	$	3.13	$	4.70	$	3.23	$	3.25
Gross proceeds	$	50,000	$	41,156	$	18,454	$	6,546
Commissions earned by Cantor	$	1,500	$	1,235	$	553	$	197
Other issuance costs	$	97	$	185	$	—	$	259