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WARRANTY COSTS AND OTHER CONTINGENCIES - Analysis of warranty accruals (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Warranty accruals:    
Balance at beginning of period $ 5,030 $ 5,410
Less: Payments made during the year (923) (767)
Add: Warranty provision for the current year 922 721
Changes to warranty provision for prior years 124 50
Balance at March 31 $ 5,153 $ 5,414