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FAIR VALUE MEASUREMENTS (Tables) | 12 Months Ended
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Dec. 31, 2020
Fair Value Disclosures [Abstract] |
Fair Value Of Marketable Securities and Investments [Table Text Block] | The fair value hierarchy of the Company’s cash equivalents and marketable securities at December 31, 2020, and 2019, was as follows:
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Fair Value Measurement at
​ | ​ | December 31, 2020
​ |  | ​ | ​ |  | Quoted Prices in |  | ​ | ​
​ | ​ | ​ | ​ | ​ | Active Markets for | ​ | Significant Other
​ | ​ | ​ | ​ | ​ | Identical Assets | ​ | Observable Inputs
(In thousands) | ​ | Total Fair Value | ​ | (Level 1) | ​ | (Level 2)
Corporate securities | ​ | $ | 146,658 | ​ | $ | — | ​ | $ | 146,658
Commercial paper | ​ |  | 253,855 | ​ |  | — | ​ |  | 253,855
Money market funds | ​ |  | 1,634 | ​ |  | 1,634 | ​ |  | —
Total | ​ | $ | 402,147 | ​ | $ | 1,634 | ​ | $ | 400,513
​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Fair Value Measurement at
​ | ​ | December 31, 2019
​ |  | ​ | ​ |  | Quoted Prices in |  | ​ | ​
​ | ​ | ​ | ​ | ​ | Active Markets for | ​ | Significant Other
​ | ​ | ​ | ​ | ​ | Identical Assets | ​ | Observable Inputs
(In thousands) | ​ | Total Fair Value | ​ | (Level 1) | ​ | (Level 2)
Corporate securities | ​ | $ | 232,398 | ​ | $ | — | ​ | $ | 232,398
Commercial paper | ​ |  | 146,955 | ​ |  | — | ​ |  | 146,955
Money market funds | ​ |  | 2,983 | ​ |  | 2,983 | ​ |  | —
Total | ​ | $ | 382,336 | ​ | $ | 2,983 | ​ | $ | 379,353

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- Definition The entire disclosure of the fair value measurement of assets and liabilities, which includes financial instruments measured at fair value that are classified in shareholders' equity, which may be measured on a recurring or nonrecurring basis. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -URI http://asc.fasb.org/topic&trid=2155941 + Details
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