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UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Parenthetical)
Jun. 30, 2019
Apr. 23, 2018
Oct. 05, 2016
Senior Unsecured Convertible Bonds Due 2018 [Member]      
Interest rate     3.25%
Senior Unsecured Convertible Bonds due 2023 [Member]      
Interest rate 4.875% 4.875% 4.875%