v3.20.4
Summary of Significant Accounting Policies - Accounts Receivable, net and Inventories (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Bad debt expense $ 100 $ 100  
Recovery recognized related to bad debt expense previously written off     $ 1,100
Inventory, Net [Abstract]      
Finished goods 9,815 17,612  
Raw materials 152 243  
Parts, supplies and other 32,382 30,441  
Total Inventories 42,349 48,296  
Inventory depreciation $ 2,000 $ 4,500  
Accounts receivable | Customer concentration      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Percentage of concentration risk 20.00% 18.00%