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SHAREHOLDERS' EQUITY (Details) |  |  |  | 4 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Oct. 16, 2020 USD ($) | Nov. 19, 2019 USD ($) | Mar. 29, 2019 USD ($) | Apr. 22, 2021 USD ($) $ / shares shares | Dec. 31, 2020 USD ($) $ / shares shares | Dec. 31, 2019 USD ($) $ / shares shares | Dec. 31, 2018 USD ($) shares | Jun. 16, 2017 $ / shares
Authorized Shares [Roll forward] |  |  |  |  |  |  |  |
Balance at beginning of period (in shares) | shares |  |  |  | 360,000,000 | 360,000,000 |  |  |
Balance at end of period (in shares) | shares |  |  |  |  | 360,000,000 | 360,000,000 |  |
Issued and Outstanding Shares [Roll forward] |  |  |  |  |  |  |  |
Balance at beginning of period, issued (in shares) | shares |  |  |  | 151,446,112 | 147,230,634 |  |  |
Balance at beginning of period, outstanding (in shares) | shares |  |  |  | 151,446,112 | 147,230,634 |  |  |
Balance at end of period, issued (in shares) | shares |  |  |  |  | 151,446,112 | 147,230,634 |  |
Balance at end of period, outstanding (in shares) | shares |  |  |  |  | 151,446,112 | 147,230,634 |  |
Common Stock [Roll forward] |  |  |  |  |  |  |  |
At-the-Market Offering, Value |  |  |  |  | $ 20,670,000 | $ 17,922,000 |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |
At-the-market offering of common Stock |  |  |  |  | 60,000,000 |  |  |
Gross amount after deducting sales commissions and other fees and expenses |  |  |  |  | 40,000,000.0 |  |  |
Net amount after deducting sales commissions and other fees and expenses |  |  |  |  | $ 38,600,000 |  |  |
Common shares issued and sold (in shares) | shares |  |  |  |  | 9,476,446 |  |  |
Proceeds from Issuance of common stock |  |  |  |  | $ 20,713,000 | $ 17,922,000 | $ 0 |
Common shares issued (in shares) | shares |  |  |  |  | 4,215,478 | 5,260,968 |  |
Additional Paid in Capital [Abstract] |  |  |  |  |  |  |  |
Reduction of share premium |  | $ (103,400,000) |  |  |  | $ 0 |  |
Share premium fund |  |  |  |  | $ 38,500,000 | 17,900,000 |  |
Contributed Surplus Account [Abstract] |  |  |  |  |  |  |  |
Reduction of contributed surplus |  |  |  |  |  |  | $ (308,800,000) |
Dividend paid |  |  |  |  | 67,200,000 | 14,300,000 |  |
Dividend charged to contribution surplus account |  |  |  |  | 27,700,000 |  |  |
Contribution to surplus account |  |  |  |  | $ 539,500,000 | $ 567,200,000 |  |
Shareholders' Rights Plan [Abstract] |  |  |  |  |  |  |  |
Common share, par value (in dollars per share) | $ / shares |  |  |  |  | $ 0.01 | $ 0.01 |  |
Subsequent Event [Member] |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |
Gross amount of at-the-market offering of common stock |  |  |  | $ 10,000,000.0 |  |  |  |
Net amount at-the-market offering of common stock |  |  |  | $ 9,700,000 |  |  |  |
Common shares issued (in shares) | shares |  |  |  | 2,989,769 |  |  |  |
Remaining available proceeds from offering |  |  |  | $ 50,000,000.0 |  |  |  |
Share price (in dollars per share) | $ / shares |  |  |  | $ 3.15 |  |  |  |
Remaining balance available, fully utilizing the new shares issued (in shares) | shares |  |  |  | 15,880,072 |  |  |  |
Maximum [Member] |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |
At-the-market offering of common Stock | $ 60,000,000 |  | $ 40,000,000 |  |  |  |  |
Shareholders' Rights Agreement [Member] |  |  |  |  |  |  |  |
Shareholders' Rights Plan [Abstract] |  |  |  |  |  |  |  |
Preferred share purchase right |  |  |  |  |  |  |  | 0.001
Common share, par value (in dollars per share) | $ / shares |  |  |  |  |  |  |  | $ 0.01
Shareholders rights, exercise price (in dollars per share) | $ / shares |  |  |  |  |  |  |  | $ 30.00
Percentage of common share ownership |  |  |  |  |  |  |  | 15.00%
Common Stock [Member] |  |  |  |  |  |  |  |
Authorized Shares [Roll forward] |  |  |  |  |  |  |  |
Balance at beginning of period (in shares) | shares |  |  |  | 360,000,000 | 360,000,000 | 360,000,000 | 180,000,000 |
Authorization of additional authorized shares (in shares) | shares |  |  |  |  |  |  | 180,000,000 |
Balance at end of period (in shares) | shares |  |  |  |  | 360,000,000 | 360,000,000 | 360,000,000 |
Issued and Outstanding Shares [Roll forward] |  |  |  |  |  |  |  |
Balance at beginning of period, issued (in shares) | shares |  |  |  | 151,446,112 | 147,230,634 | 141,969,666 | 141,969,666 |
Balance at beginning of period, outstanding (in shares) | shares |  |  |  | 151,446,112 | 147,230,634 | 141,969,666 | 141,969,666 |
At-the-Market Offering (in shares) | shares |  |  |  |  | 4,215,478 | 5,260,968 |  |
Balance at end of period, issued (in shares) | shares |  |  |  |  | 151,446,112 | 147,230,634 | 141,969,666 |
Balance at end of period, outstanding (in shares) | shares |  |  |  |  | 151,446,112 | 147,230,634 | 141,969,666 |
Common Stock [Roll forward] |  |  |  |  |  |  |  |
Balance at beginning of period |  |  |  | $ 1,514,000 | $ 1,472,000 | $ 1,420,000 | $ 1,420,000 |
At-the-Market Offering, Value |  |  |  |  | 42,000 | 52,000 |  |
Balance at end of period |  |  |  |  | 1,514,000 | 1,472,000 | $ 1,420,000 |
Common Stock [Abstract] |  |  |  |  |  |  |  |
At-the-market offering of common Stock |  |  |  |  | $ 40,000,000 | 40,000,000 |  |
Additional Paid in Capital [Abstract] |  |  |  |  |  |  |  |
Reduction of share premium |  |  |  |  |  | $ 0 |  |

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