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Commitments and Contingencies - Warranty (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Warranty      
Warranty period of products purchased 1 year    
Balance, beginning of the year $ 6,532 $ 4,217 $ 8,159
Warranties issued 6,737 5,817 3,916
Addition from Ultratech acquisition   1,889  
Consumption of reserves (6,573) (6,330) (6,433)
Changes in estimate 1,156 939 (1,425)
Balance, end of the year $ 7,852 $ 6,532 $ 4,217