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Valuation and Qualifying Accounts (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at Beginning of Year $ 2,748 $ 14,410 $ 13,756
Changes Charged to Statement of Income Accounts 1,575 2,257 2,624
Inventory Write-down 0 (13,919) (1,970)
Balance at End of Year $ 4,323 $ 2,748 $ 14,410