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Basis of Presentation - Customer concentration (Details)
3 Months Ended
Mar. 31, 2022
customer
item
Mar. 31, 2021
Customer concentration    
Number of top customers 10  
Number of calendar years in which top customers typically generate minimum specified percentage of revenue | item 1  
Revenues | Customer concentration | Top ten customers    
Customer concentration    
Number of top customers 10  
Percentage of concentration risk 45.40% 45.40%
Revenues | Customer concentration | Top ten customers | Minimum    
Customer concentration    
Minimum percentage of revenues generated by top ten customers 40.00%  
Revenues | Customer concentration | Top ten customers | Maximum    
Customer concentration    
Minimum percentage of revenues generated by top ten customers 50.00%  
Revenues | Customer concentration | Solar energy customer    
Customer concentration    
Percentage of concentration risk   10.10%
Number of customers 1