Etratech Acquisition - Summary of Amortization Expense (Detail) - Etratech Inc. - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2018
Business Acquisition [Line Items]
Amortization of intangibles	$ 943	$ 2,790
Product revenues
Business Acquisition [Line Items]
Amortization of intangibles	528	1,562
Cost of sales
Business Acquisition [Line Items]
Amortization of intangibles	$ 415	$ 1,228

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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