Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Credit Risk (Details)

v3.19.3.a.u2
Summary of Significant Accounting Policies - Credit Risk (Details) - Sales - Customer concentration
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Concentrations of Credit Risk      
Sales to major customers (as a percent) 100.00% 100.00% 100.00%
Company A      
Concentrations of Credit Risk      
Sales to major customers (as a percent) 16.00% 8.00% 4.00%
Company B      
Concentrations of Credit Risk      
Sales to major customers (as a percent) 15.00% 6.00% 14.00%
Company C      
Concentrations of Credit Risk      
Sales to major customers (as a percent) 9.00% 13.00% 20.00%
Company D      
Concentrations of Credit Risk      
Sales to major customers (as a percent) 3.00% 14.00%  
All others      
Concentrations of Credit Risk      
Sales to major customers (as a percent) 57.00% 59.00% 62.00%