Liquidity and Ability to Continue as a Going Concern	6 Months Ended
Jun. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Liquidity and Ability to Continue as a Going Concern	Liquidity and Ability to Continue as a Going Concern The Company is subject to a number of risks similar to those of earlier stage commercial companies, including dependence on key individuals and products, the difficulties inherent in the development of a commercial market, the potential need to obtain additional capital, competition from larger companies, other technology companies and other technologies. In accordance with ASC 205-40, Going Concern, the Company has evaluated whether there are conditions or events, considered in the aggregate, that raise substantial doubt about the Company's ability to continue as a going concern within one year after the date that the consolidated financial statements are issued. As of June 30, 2019, the Company had $27.3 million in cash and cash equivalents ($0.5 million of which is restricted cash). The Company has incurred losses each year since inception and has experienced negative cash flows from operations in each year since inception and has an accumulated deficit of $548.6 million as of June 30, 2019. The Company's Term Loan (as defined below) includes a liquidity covenant whereby the Company must maintain a cash balance greater than $2.0 million. Based on its current business plan assumptions and expected cash burn rate, excluding potential share sales associated with its financing agreements discussed below, the Company believes that it has sufficient cash and cash equivalents to fund its current operations into the first quarter of 2020. These factors raise substantial doubt regarding the Company's ability to continue as a going concern. On January 26, 2018, the Company entered into an At the Market Issuance Sales Agreement (the “Sales Agreement”) with B. Riley FBR, Inc. (“FBR”) under which the Company may, from time to time in its sole discretion, issue and sell through FBR, acting as agent, shares of the Company’s common stock (the “Placement Shares”) up to the amount currently authorized in an effective registration statement. FBR has the option to decline any sales orders at its discretion. The issuance and sale of the Placement Shares are made pursuant to the terms of the Sales Agreement and a prospectus supplement on Form S-3, dated March 22, 2019, to the Company’s Shelf Registration Statement on Form S-3 (File No. 333-220799), which was filed with the Securities and Exchange Commission (“SEC”) on October 4, 2017, and declared effective by the SEC on December 15, 2017, which provides for the sale and issuance of up to approximately $10.3 million of Placement Shares. During the six months ended June 30, 2019, the Company sold 988,976 shares at an average $4.83 per share and received net proceeds of $4.6 million. During the third quarter of 2019 through August 7, 2019, the Company sold an additional 1,169,415 shares at an average of $3.99 per share for net proceeds of $4.5 million. As of August 7, 2019, the Company has $0.8 million remaining available for sale under the current prospectus supplement, pursuant to the Sales Agreement. On June 11, 2018, the Company entered into a purchase agreement (the “Second Purchase Agreement”) with Aspire Capital Fund, LLC (“Aspire Capital”), pursuant to which the Company has the right, in its sole discretion, to present Aspire Capital with a purchase notice, directing Aspire Capital (as principal) to purchase up to 7,500 shares of the Company’s common stock per business day, in an aggregate amount of up to $21.0 million of the Company's common stock (the “Purchase Shares”). At the 2019 annual meeting of stockholders (the “Annual Meeting”) held on May 16, 2019 the stockholders approved pursuant to Nasdaq Listing rules 5635(b) and 5635(d) the potential issuance of shares of the Company's common stock, to Aspire Capital of up to $21.0 million under the Second Purchase Agreement. As a result, the Second Purchase Agreement exchange cap restricting the amount of shares that may be sold to Aspire Capital was removed. The purchase agreement provides that the Company and Aspire Capital shall not effect any sales under the closing sale price of its common stock that is less than $1.00. For the three and six months ended June 30, 2019, the company sold no shares under the Second Purchase Agreement. As of June 30, 2019, the Company has $19.7 million remaining available to sell under the Second Purchase Agreement. The Company completed a public offering on November 16, 2018 for net proceeds of approximately $32.5 million, after deducting underwriting discounts and commissions of $2.7 million and offering expenses of $0.8 million. This offering also included 3,750,000 Series A warrants and 3,750,000 Series B warrants. The Series A warrants, if exercised at the exercise price of $12.00 per share prior to their expiration date of five years after issuance, could generate an additional $45.0 million before fees. The Series B warrants, if exercised at the exercise price of $9.60 per share prior to their expiration date of nine months after issuance, could generate $36.0 million before fees. As of June 30, 2019 a total of 2,096 Series B warrants were exercised at $9.60 per share for de minimis net proceeds. There is uncertainty regarding the utilization of financing associated from the Sales Agreement and the Second Purchase Agreement, as well as the ability to receive proceeds from the exercise of the Series A and B warrants. This uncertainty makes our ability to provide enough cash to fund operations beyond the first quarter of 2020 unknown. The Company is actively pursuing additional sources of financing to fund its operations. The Company can provide no assurances that additional financings will be consummated on acceptable terms, or at all. If the Company is unable to effect a sufficient financing or capital raise, there could be a material adverse effect on the Company. These consolidated financial statements have been prepared with the assumption that the Company will continue as a going concern and will be able to realize its assets and discharge its liabilities in the normal course of business and do not include any adjustments to reflect the possible future effects on the recoverability and classification of assets or the amounts and classification of liabilities that may result from the inability of the Company to continue as a going concern.

Liquidity and Ability to Continue as a Going Concern

The Company is subject to a number of risks similar to those of earlier stage commercial companies, including dependence on key individuals and products, the difficulties inherent in the development of a commercial market, the potential need to obtain additional capital, competition from larger companies, other technology companies and other technologies.

In accordance with ASC 205-40, Going Concern, the Company has evaluated whether there are conditions or events, considered in the aggregate, that raise substantial doubt about the Company's ability to continue as a going concern within one year after the date that the consolidated financial statements are issued. As of June 30, 2019, the Company had $27.3 million in cash and cash equivalents ($0.5 million of which is restricted cash). The Company has incurred losses each year since inception and has experienced negative cash flows from operations in each year since inception and has an accumulated deficit of $548.6 million as of June 30, 2019. The Company's Term Loan (as defined below) includes a liquidity covenant whereby the Company must maintain a cash balance greater than $2.0 million. Based on its current business plan assumptions and expected cash burn rate, excluding potential share sales associated with its financing agreements discussed below, the Company believes that it has sufficient cash and cash equivalents to fund its current operations into the first quarter of 2020. These factors raise substantial doubt regarding the Company's ability to continue as a going concern.

On January 26, 2018, the Company entered into an At the Market Issuance Sales Agreement (the “Sales Agreement”) with B. Riley FBR, Inc. (“FBR”) under which the Company may, from time to time in its sole discretion, issue and sell through FBR, acting as agent, shares of the Company’s common stock (the “Placement Shares”) up to the amount currently authorized in an effective registration statement. FBR has the option to decline any sales orders at its discretion. The issuance and sale of the Placement Shares are made pursuant to the terms of the Sales Agreement and a prospectus supplement on Form S-3, dated March 22, 2019, to the Company’s Shelf Registration Statement on Form S-3 (File No. 333-220799), which was filed with the Securities and Exchange Commission (“SEC”) on October 4, 2017, and declared effective by the SEC on December 15, 2017, which provides for the sale and issuance of up to approximately $10.3 million of Placement Shares. During the six months ended June 30, 2019, the Company sold 988,976 shares at an average $4.83 per share and received net proceeds of $4.6 million. During the third quarter of 2019 through August 7, 2019, the Company sold an additional 1,169,415 shares at an average of $3.99 per share for net proceeds of $4.5 million. As of August 7, 2019, the Company has $0.8 million remaining available for sale under the current prospectus supplement, pursuant to the Sales Agreement.

On June 11, 2018, the Company entered into a purchase agreement (the “Second Purchase Agreement”) with Aspire Capital Fund, LLC (“Aspire Capital”), pursuant to which the Company has the right, in its sole discretion, to present Aspire Capital with a purchase notice, directing Aspire Capital (as principal) to purchase up to 7,500 shares of the Company’s common stock per business day, in an aggregate amount of up to $21.0 million of the Company's common stock (the “Purchase Shares”). At the 2019 annual meeting of stockholders (the “Annual Meeting”) held on May 16, 2019 the stockholders approved pursuant to Nasdaq Listing rules 5635(b) and 5635(d) the potential issuance of shares of the Company's common stock, to Aspire Capital of up to $21.0 million under the Second Purchase Agreement. As a result, the Second Purchase Agreement exchange cap restricting the amount of shares that may be sold to Aspire Capital was removed. The purchase agreement provides that the Company and Aspire Capital shall not effect any sales under the closing sale price of its common stock that is less than $1.00. For the three and six months ended June 30, 2019, the company sold no shares under the Second Purchase Agreement. As of June 30, 2019, the Company has $19.7 million remaining available to sell under the Second Purchase Agreement.

The Company completed a public offering on November 16, 2018 for net proceeds of approximately $32.5 million, after deducting underwriting discounts and commissions of $2.7 million and offering expenses of $0.8 million. This offering also included 3,750,000 Series A warrants and 3,750,000 Series B warrants. The Series A warrants, if exercised at the exercise price of $12.00 per share prior to their expiration date of five years after issuance, could generate an additional $45.0 million before fees. The Series B warrants, if exercised at the exercise price of $9.60 per share prior to their expiration date of nine months after issuance, could generate $36.0 million before fees. As of June 30, 2019 a total of 2,096 Series B warrants were exercised at $9.60 per share for de minimis net proceeds.

There is uncertainty regarding the utilization of financing associated from the Sales Agreement and the Second Purchase Agreement, as well as the ability to receive proceeds from the exercise of the Series A and B warrants. This uncertainty makes our ability to provide enough cash to fund operations beyond the first quarter of 2020 unknown. The Company is actively pursuing additional sources of financing to fund its operations. The Company can provide no assurances that additional financings will be consummated on acceptable terms, or at all. If the Company is unable to effect a sufficient financing or capital raise, there could be a material adverse effect on the Company.

These consolidated financial statements have been prepared with the assumption that the Company will continue as a going concern and will be able to realize its assets and discharge its liabilities in the normal course of business and do not include any adjustments to reflect the possible future effects on the recoverability and classification of assets or the amounts and classification of liabilities that may result from the inability of the Company to continue as a going concern.