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Financial Instruments Financial Instruments narrative (Details) - USD ($)
$ in Thousands
Dec. 31, 2018
May 01, 2018
Dec. 31, 2017
Discount rate   8.42%  
Convertible Debt, Fair Value Disclosures   $ 651,300  
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value $ 1,117,175   $ 2,169,197
Available-for-sale Debt Securities Gross Unrealized Gain 100    
Due 2023 [Member]      
Debt Instrument, Fair Value Disclosure 741,300    
Due 2025 [Member]      
Debt Instrument, Fair Value Disclosure 502,200    
Due 2027      
Debt Instrument, Fair Value Disclosure $ 524,200