Shelf Registration Statement	3 Months Ended
Mar. 31, 2019
Stock Offering [Abstract]
Shelf Registration Statement	Shelf Registration Statement On November 9, 2017, the Company filed a shelf registration statement on Form S-3 with the SEC to, from time to time, sell up to an aggregate of $125 million of any combination of its common stock, warrants, debt securities or units. On November 16, 2017, the registration statement was declared effective by the SEC, which will allow the Company to access the capital markets for the three-year period following this effective date. Net proceeds, terms and pricing of each offering of securities issued under the shelf registration statement will be determined at the time of such offerings. In August 2018, under the shelf registration statement, the Company completed a public offering of 7,590,000 shares of its common stock at a public offering price of $3.25 per share. The Company received total net proceeds of approximately $23.0 million from the offering, after deducting underwriting discounts, commissions and offering expenses. As of March 31, 2019, $24.7 million of securities have been issued under the shelf registration statement and a balance of $100.3 million remains available for future issuance; provided, however, that pursuant to the terms of the Merger Agreement, the Company is required, except in limited circumstances, to obtain the consent of Tesla in order to issue equity securities, which such consent shall not be unreasonably withheld.

Shelf Registration Statement

On November 9, 2017, the Company filed a shelf registration statement on Form S-3 with the SEC to, from time to time, sell up to an aggregate of $125 million of any combination of its common stock, warrants, debt securities or units. On November 16, 2017, the registration statement was declared effective by the SEC, which will allow the Company to access the capital markets for the three-year period following this effective date. Net proceeds, terms and pricing of each offering of securities issued under the shelf registration statement will be determined at the time of such offerings.

In August 2018, under the shelf registration statement, the Company completed a public offering of 7,590,000 shares of its common stock at a public offering price of $3.25 per share. The Company received total net proceeds of approximately $23.0 million from the offering, after deducting underwriting discounts, commissions and offering expenses. As of March 31, 2019, $24.7 million of securities have been issued under the shelf registration statement and a balance of $100.3 million remains available for future issuance; provided, however, that pursuant to the terms of the Merger Agreement, the Company is required, except in limited circumstances, to obtain the consent of Tesla in order to issue equity securities, which such consent shall not be unreasonably withheld.