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Consolidated Statements Of Stockholders' Equity (Parenthetical) - Convertible Notes [Member]
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
3.25% Convertible Notes Due 2018 [Member]      
Interest rate, stated percentage     3.25%
3.25% Convertible Notes Due 2019 [Member]      
Interest rate, stated percentage   3.25% 3.25%
Corporate Activities [Member] | 4.00% Convertible Notes Due 2024 [Member]      
Interest rate, stated percentage 4.00% 4.00%