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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Product Warranty (Details 3) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Movement in Standard and Extended Product Warranty, Increase (Decrease) [Roll Forward]    
Accrual at beginning of the year $ 2,821 $ 3,140
Provision 2,618 1,750
Settlement and Other (2,292) (2,069)
Accrual at end of year $ 3,147 $ 2,821