CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) shares in Thousands, $ in Thousands | Total | Convertible Preferred Stock [Member] | Common Stock [Member] | Additional Paid-In Capital [Member] | Accumulated Other Comprehensive Income (Loss) [Member] | Accumulated Deficit [Member] |
Beginning Balance at Dec. 31, 2018 | $ 3,993 | | $ 20,998 | $ 4 | $ 642,460 | | $ (659,469) |
Beginning Balance, shares at Dec. 31, 2018 | | | 18 | 37,474 | | | |
Issuance of common and preferred stock in underwritten offering, net of issuance costs | 18,536 | | $ 7,877 | $ 2 | 10,657 | | |
Issuance of common and preferred stock in underwritten offering, net of issuance costs, shares | | | 17 | 23,000 | | | |
Conversion of preferred stock to common stock | | | $ (21,762) | $ 1 | 21,761 | | |
Conversion of preferred stock to common stock, shares | | | (23) | 11,950 | | | |
Issuance of common stock from vesting of restricted stock awards | 54 | | | | 54 | | |
Issuance of common stock from vesting of restricted stock awards, shares | | | | 104 | | | |
Issuance of common stock through controlled equity offering facilities, net of issuance cost | 464 | | | | 464 | | |
Issuance of common stock through controlled equity offering facilities, net of issuance cost, shares | | | | 398 | | | |
Issuance of common stock under employee stock purchase plans | 36 | | | | 36 | | |
Issuance of common stock under employee stock purchase plans, shares | | | | 61 | | | |
Stock-based compensation expenses | 757 | | | | 757 | | |
Net loss | (12,101) | | | | | | (12,101) |
Ending Balance at Jun. 30, 2019 | 11,739 | | $ 7,113 | $ 7 | 676,189 | | (671,570) |
Ending Balance, shares at Jun. 30, 2019 | | | 12 | 72,987 | | | |
Beginning Balance at Mar. 31, 2019 | 17,086 | | $ 25,647 | $ 7 | 656,761 | | (665,329) |
Beginning Balance, shares at Mar. 31, 2019 | | | 28 | 67,578 | | | |
Conversion of preferred stock to common stock | | | $ (18,534) | | 18,534 | | |
Conversion of preferred stock to common stock, shares | | | (16) | 4,950 | | | |
Issuance of common stock through controlled equity offering facilities, net of issuance cost | 464 | | | | 464 | | |
Issuance of common stock through controlled equity offering facilities, net of issuance cost, shares | | | | 398 | | | |
Issuance of common stock under employee stock purchase plans | 36 | | | | 36 | | |
Issuance of common stock under employee stock purchase plans, shares | | | | 61 | | | |
Stock-based compensation expenses | 394 | | | | 394 | | |
Net loss | (6,241) | | | | | | (6,241) |
Ending Balance at Jun. 30, 2019 | 11,739 | | $ 7,113 | $ 7 | 676,189 | | (671,570) |
Ending Balance, shares at Jun. 30, 2019 | | | 12 | 72,987 | | | |
Beginning Balance at Dec. 31, 2019 | 27,543 | [1] | $ 11,769 | $ 11 | 698,562 | $ 1 | (682,800) |
Beginning Balance, shares at Dec. 31, 2019 | | | 20 | 111,393 | | | |
Issuance of common stock under employee stock purchase plans | 23 | | | | 23 | | |
Issuance of common stock under employee stock purchase plans, shares | | | | 72 | | | |
Stock-based compensation expenses | 706 | | | | 706 | | |
Net loss | (12,165) | | | | | | (12,165) |
Unrealized loss on available-for-sale securities | (1) | | | | | $ (1) | |
Ending Balance at Jun. 30, 2020 | 16,106 | | $ 11,769 | $ 11 | 699,291 | | (694,965) |
Ending Balance, shares at Jun. 30, 2020 | | | 20 | 111,465 | | | |
Beginning Balance at Mar. 31, 2020 | 22,086 | | $ 11,769 | $ 11 | 698,881 | | (688,575) |
Beginning Balance, shares at Mar. 31, 2020 | | | 20 | 111,393 | | | |
Issuance of common stock under employee stock purchase plans | 23 | | | | 23 | | |
Issuance of common stock under employee stock purchase plans, shares | | | | 72 | | | |
Stock-based compensation expenses | 387 | | | | 387 | | |
Net loss | (6,390) | | | | | | (6,390) |
Ending Balance at Jun. 30, 2020 | $ 16,106 | | $ 11,769 | $ 11 | $ 699,291 | | $ (694,965) |
Ending Balance, shares at Jun. 30, 2020 | | | 20 | 111,465 | | | |
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[1] | The condensed consolidated balance sheet as of December 31, 2019, has been derived from the audited financial statements as of that date included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019. |