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Summary of Significant Accounting Policies and Other Items - Significant Customers and Concentration of Credit Risk (Details)
$ in Millions
12 Months Ended
Dec. 31, 2019
USD ($)
customer
Dec. 31, 2018
USD ($)
customer
Dec. 31, 2017
USD ($)
customer
Total revenues | Customer      
Significant Customers and Concentration of Credit Risk      
Number of Customers | customer 1 1 1
Concentration of risk (as a percent) 10.00% 11.00% 11.00%
Purchases | Supplier concentration      
Significant Customers and Concentration of Credit Risk      
Concentration of risk (as a percent) 16.00% 21.00% 22.00%
Purchases from the vendor $ 36.5 $ 46.7 $ 33.4
Amounts due to the vendor $ 4.3 $ 5.0