Annual report pursuant to Section 13 and 15(d)

Property, plant and equipment, net - Depreciation Expense (Details)

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Property, plant and equipment, net - Depreciation Expense (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Property, plant and equipment, net      
Depreciation expense $ 6,627,000 $ 7,172,000 $ 7,188,000