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SHAREHOLDERS' EQUITY (Tables) | 12 Months Ended
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Dec. 31, 2019
Summary of information about stock options under the Plan | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | ​ | ​ |  | Weighted |  | ​ | ​ |
​ | ​ | ​ | ​ | Weighted | ​ | Average | ​ | ​ | ​ |
​ | ​ | ​ | ​ | Average | ​ | Remaining | ​ | ​ | ​ |
​ | ​ | Number of | ​ | Exercise | ​ | Contractual | ​ | Intrinsic |
​ | ​ | Shares | ​ | Price | ​ | Life (Years) | ​ | Value |
​ | ​ | (in thousands, except per share and year data) |
Balance at December 31, 2016 |  | 4,720 | ​ | $ | 2.41 |  | 3.4 | ​ | $ | 4,388 | ​
Granted |  | 338 | ​ | ​ | 2.99 | ​ | — | ​ | ​ | — | ​
Exercised |  | (94) | ​ | ​ | 1.30 | ​ | — | ​ | ​ | 87 | ​
Forfeited | ​ | (37) | ​ | ​ | 4.28 | ​ | — | ​ | ​ | — | ​
Expired | ​ | (21) | ​ | ​ | 5.00 | ​ | — | ​ | ​ | — | ​
Balance at December 31, 2017 |  | 4,906 | ​ | $ | 2.45 |  | 2.6 | ​ | $ | 2,564 | ​
Granted |  | 375 | ​ | ​ | 1.90 | ​ | — | ​ | ​ | — | ​
Exercised |  | (171) | ​ | ​ | 1.02 | ​ | — | ​ | ​ | 195 | ​
Forfeited |  | (405) | ​ | ​ | 3.99 | ​ | — | ​ | ​ | — | ​
Expired |  | (462) | ​ | ​ | 2.27 | ​ | — | ​ | ​ | — | ​
Balance at December 31, 2018 |  | 4,243 | ​ | $ | 2.33 |  | 2.0 | ​ | $ | 1,475 | ​
Granted |  | 3,050 | ​ | ​ | 1.73 | ​ | — | ​ | ​ | — | ​
Exercised |  | (535) | ​ | ​ | 1.01 | ​ | — | ​ | ​ | 419 | ​
Forfeited |  | (700) | ​ | ​ | 2.56 | ​ | — | ​ | ​ | — | ​
Expired | ​ | (789) | ​ | ​ | 2.90 | ​ | — | ​ | ​ | — | ​
Balance at December 31, 2019 |  | 5,269 | ​ | $ | 2.00 |  | 3.0 | ​ | $ | 364 | ​
Exercisable at December 31, 2019 |  | 2,234 | ​ | $ | 2.27 |  | 1.2 | ​ | $ | 364 | ​
Schedule of weighted-average assumptions used for estimation of the fair value of the options granted under the Plan at the date of grant, using the Black-Scholes Option Valuation Model | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ | 2019 | ​ | ​ | 2018 | ​ | ​ | 2017
Risk-free interest rate | ​ | ​ | 1.45% to 1.87% | ​ | ​ | 2.67% to 2.89% | ​ | ​ | 1.46% to 1.60%
Dividend yield | ​ | ​ | 0.00% | ​ | ​ | 0.36% to 0.53% | ​ | ​ | 0.31% to 0.36%
Volatility factor of the expected market price of common stock | ​ | ​ | 58% | ​ | ​ | 63% to 64% | ​ | ​ | 72% to 74%
Weighted-average expected life of option | ​ | ​ | 3.5 years | ​ | ​ | 3.5 years | ​ | ​ | 3.5 years
Weighted-average grant date fair value | ​ | $ | 1.73 | ​ | $ | 1.90 | ​ | $ | 2.99
Summary of status and activity of non-vested stock options | ​
​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | Weighted
​ | ​ | ​ | ​ | Average
​ | ​ | Number of | ​ | Grant Date
​ |  | Shares |  | Fair Value
​ | ​ | (in thousands, except per share amounts)
Non-vested, beginning of year | ​ | 691 | ​ | $ | 1.28
Granted | ​ | 3,050 | ​ | $ | 0.58
Cancelled/Forfeited | ​ | (402) | ​ | $ | 0.74
Vested | ​ | (304) | ​ | $ | 1.44
Non-vested, end of year | ​ | 3,035 | ​ | $ | 0.64
November 2019 Offering |
Schedule of Black-Scholes pricing model to determine the fair value of warrants | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | November 20, 2019 | ​
Risk-free interest rate | ​ | ​ | ​ | ​ | ​ | 1.55 | %
Dividend yield | ​ | ​ | ​ | ​ | ​ | 0.00 | %
Volatility factor of the expected market price of common stock | ​ | ​ | ​ | ​ | ​ | 60 | %
Weighted-average expected life | ​ | ​ | ​ | ​ | ​ | 5 years | ​
Weighted-average grant date fair value | ​ | ​ | ​ | ​ | $ | 0.52 | ​
March 2019 Offering |
Schedule of Black-Scholes pricing model to determine the fair value of warrants | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Issued on: | March 29, 2019 | ​ | ​ | May 23, 2019 | ​
Risk-free interest rate | ​ | 2.30 | % | ​ | ​ | 2.14 | %
Dividend yield | ​ | 0.00 | % | ​ | ​ | 0.00 | %
Volatility factor of the expected market price of common stock | ​ | 50 | % | ​ | ​ | 45 | %
Weighted-average expected life | ​ | 3 years | ​ | ​ | ​ | 3 years | ​
Weighted-average grant date fair value | $ | 0.43 | ​ | ​ | $ | 0.22 | ​
September 2017 Offering |
Schedule of Black-Scholes pricing model to determine the fair value of warrants | ​
​ | ​ | ​ | ​
Risk-free interest rate | ​ | 1.56 | %
Dividend yield | ​ | 0.36 | %
Volatility factor of the expected market price of common stock | ​ | 71 | %
Weighted-average expected life | ​ | 53 weeks | ​
Weighted-average grant date fair value | $ | 0.40 | ​

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- Definition Tabular disclosure of input and valuation technique used to measure fair value and change in valuation approach and technique for each separate class of asset and liability measured on recurring and nonrecurring basis. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
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- Definition Tabular disclosure of the changes in outstanding nonvested shares. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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