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STOCK-BASED COMPENSATION PLANS (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
STOCK-BASED COMPENSATION PLANS |  |
Recognized employee stock-based compensation expense | $ 8,900,000 | $ 9,600,000
Employee Stock Purchase Plan |  |
STOCK-BASED COMPENSATION PLANS |  |
Shares available for grant | 1,161,220 |
Weighted-Average Grant Date Fair Value |  |
Shares available under the plan | 3,600,000 |
Offering period for the plan (in months) | 3 months |
Period of interval between occurrence of purchases (in months) | 3 months |
IRS regulated cap for payroll deduction to purchase common stock | $ 25,000 |
Purchase price expressed as a percentage of fair market value of common stock (as a percent) | 90.00% |
Shares issued under ESPP | 237,726 |
Shares available for purchase under ESPP | 1,161,220 |
Minimum | Employee Stock Purchase Plan |  |
Weighted-Average Grant Date Fair Value |  |
Eligible service period of employees per week to participate in the plan (in hours) | 20 hours |
Eligible service period of employees in a calendar year to participate in the plan (in months) | 5 months |
Percentage of employees' eligible earnings as payroll deduction to purchase common stock | 1.00% |
Maximum | Employee Stock Purchase Plan |  |
Weighted-Average Grant Date Fair Value |  |
Percentage of employees' eligible earnings as payroll deduction to purchase common stock | 10.00% |
2007 Equity Incentive Plan |  |
STOCK-BASED COMPENSATION PLANS |  |
Shares available for grant | 3,455,800 |
Weighted-Average Grant Date Fair Value |  |
Total fair value RSUs vested (in dollars) | $ 9,700,000 | $ 10,100,000
Unrecognized compensation cost related to the RSUs | $ 8,800,000 |
2007 Equity Incentive Plan | Maximum |  |
STOCK-BASED COMPENSATION PLANS |  |
Expiration period (in years) | 10 years |
2007 Equity Incentive Plan | Restricted stock units |  |
STOCK-BASED COMPENSATION PLANS |  |
Percentage of relevant period has elapsed for pro rata vesting of the awards | 50.00% |
RSU |  |
Non-vested at the beginning of the period (in shares) | 5,575,000 | 4,757,000
Granted (in shares) | 4,249,000 | 3,838,000
Vested (in shares) | (2,634,000) | (2,564,000)
Forfeited (in shares) | (324,000) | (456,000)
Non-vested at the end of the period (in shares) | 6,866,000 | 5,575,000
Weighted-Average Grant Date Fair Value |  |
Non-vested at the beginning of the period (in dollars per share) | $ 3.22 | $ 3.98
Granted (in dollars per share) | 2.01 | 2.93
Vested (in dollars per share) | 3.68 | 3.94
Forfeited (in dollars per share) | 3.00 | 4.08
Non-vested at the end of the period (in dollars per share) | $ 2.31 | $ 3.22
Weighted-average period to recognize unrecognized compensation cost | 2 years 1 month 6 days |
2007 Equity Incentive Plan | Restricted stock units | Awards Vesting On Employment Through The Fourth Anniversary Of Grant |  |
STOCK-BASED COMPENSATION PLANS |  |
Award vesting percentage | 100.00% |
2007 Equity Incentive Plan | Restricted stock units | Awards Vesting On Change In Control |  |
STOCK-BASED COMPENSATION PLANS |  |
Award vesting percentage | 100.00% |
Incentive Plan Amendment |  |
STOCK-BASED COMPENSATION PLANS |  |
Additional shares authorized | 5,500,000 |

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- Definition Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options. + 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 (i) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period. + 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)(1)(iv)(3) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event. + 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)(iii)(3) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + 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)(iii)(1) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + 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)(iii)(1) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. + 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)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options. + 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)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period. + 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)(iii)(2) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash. + 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)(2) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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