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Significant Accounting Policies, Convertible Debt (Details)
Jun. 30, 2020
Dec. 31, 2019
Jun. 30, 2019
0.125 Percent Convertible Senior Notes [Member]      
Convertible Debt [Abstract]      
Interest rate on convertible senior notes 0.125% 0.125%  
1 Percent Convertible Senior Notes [Member]      
Convertible Debt [Abstract]      
Interest rate on convertible senior notes 1.00% 1.00% 1.00%