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Warrants | 12 Months Ended
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Dec. 31, 2018
Notes To Financial Statements [Abstract] |
Warrants | 13. WARRANTS As more fully described in Notes 8 and 10, the Company completed a series of equity and debt financing transactions in 2018 and 2017 that included the issuance of warrants to purchase 190,114 and 9,231,628 shares, respectively, of the Company’s common stock. During 2018, the Company and certain investors holding warrants to collectively purchase 1.6 million shares of the Company’s common stock, which were received in the February 2017 Public Offering and the October 2017 Underwritten Offering, entered into warrant exchange agreements whereby the Company issued 820,714 shares of its common stock in exchange for the cancellation of the warrants. Investors exercised warrants to purchase 7,617,148 shares of common stock providing $22.0 million in gross proceeds to the Company during 2017. Warrants to purchase 13,927 and 44,037 shares of common stock expired during 2018 and 2017, respectively. After the warrant exchange, warrants outstanding totaled approximately 1.6 million with a weighted average exercise price of $5.75 per share as of December 31, 2018. Approximately 1.2 million of these outstanding warrants with a strike price of $6.20 per share will expire on April 4, 2019. Following is a summary of all warrant activity for the two years ended December 31, 2018:
Warrants |  | Number of Warrants Issued |  |  | Weighted Average Exercise Price |
Warrants outstanding at January 1, 2017 |  |  | 1,487,958 |  |  | $ | 9.39 |
Warrants issued in connection with 2017 equity transactions |  |  | 9,231,628 |  |  | $ | 3.46 |
Warrants exercised during 2017 |  |  | (7,617,147 | ) |  | $ | 2.89 |
Warrants expired during 2017 |  |  | (44,037 | ) |  | $ | 209.23 |
Warrants outstanding at December 31, 2017 |  |  | 3,058,402 |  |  | $ | 5.29 |
Warrants issued in connection with 2018 debt transaction |  |  | 190,114 |  |  | $ | 2.63 |
Warrants cancelled in exchange for common stock |  |  | (1,641,427 | ) |  | $ | 3.04 |
Warrants expired during 2018 |  |  | (13,927 | ) |  | $ | 226.24 |
Warrants outstanding and exercisable at December 31, 2018 |  |  | 1,593,162 |  |  | $ | 5.36 |
Aggregate intrinsic value of outstanding warrants at December 31, 2018 |  | $ | - |  |  |  |  |
Weighted average remaining contractual terms (years) |  |  | 1.87 |  |  |  |  |

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