Shareholders' Equity

3 Months Ended

Mar. 31, 2018

Stockholders' Equity Note [Abstract]

Shareholders' Equity

Shareholders' Equity

At-the-Market Sales Agreement

On October 10, 2016, the Company entered into its at-the-market sales agreement with Cowen (ATM Agreement), pursuant to which the Company may sell shares of its common stock through Cowen, as sales agent, in registered transactions from the Company's shelf registration statement filed in June 2015, for aggregate proceeds of up to $25.0 million.  Shares of common stock sold under the ATM are to be sold at market prices.  The Company will pay up to 3% of the gross proceeds to Cowen as a commission. A total of 2,340,879 shares of common stock have been sold under the ATM Agreement of which 1,983,023 were sold in 2017 for proceeds of $7.2 million (net of $0.3 million in commission and issuance costs) and as of March 31, 2018 had remaining capacity of approximately $16.7 million. There were no shares sold under the ATM Agreement during the three months endedMarch 31, 2018.