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Common stock Common stock issuance (Details 2) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Class of Stock [Line Items] |  |  |
Common Stock, Shares Authorized | 500,000,000 | 500,000,000 |
Common Stock, Shares, Issued | 201,061,198 | 200,922,790 |
Proceeds from Issuance of Common Stock | $ 3,385,000 | $ 106,848,000 | $ 0
At-the-market offering |  |  |
Class of Stock [Line Items] |  |  |
Common Stock, Shares Authorized | 6,400,000 |  |
Common Stock, Shares, Issued | 0 | 3,600,000 |
Proceeds from Issuance of Common Stock |  | $ 94,000,000.0 |
Sales Commissions Paid from Issuance of Common Stock through the ATM Program |  | $ 950,000 |
Common Stock, Authorized Shares Remaining | 6,400,000 |  |
K-Plan |  |  |
Class of Stock [Line Items] |  |  |
Common Stock, Authorized Shares Remaining | 7,200,000 |  |

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- Definition Aggregate number of common shares reserved for future issuance. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.29) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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