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Segment, Product and Geographic Information - Accounts receivable from significant customers (Details) - USD ($)
$ in Thousands
Dec. 31, 2019
Dec. 31, 2018
Disclosure of operating segments [line items]    
Accounts receivable $ 75,222 $ 87,963
Customer A and Its Affiliates [Member]    
Disclosure of operating segments [line items]    
Accounts receivable 62,136 63,501
Customer B and Its Affiliates [Member]    
Disclosure of operating segments [line items]    
Accounts receivable $ 13,086 $ 24,462