Goodwill and Acquired Intangibles (Details 2) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Amortization of acquired intangibles
Cost of product and maintenance	$ 11,447	$ 9,925	$ 33,791	$ 31,078
Amortization of acquired intangibles	4,438	2,874	13,234	9,341
Total amortization of acquired intangibles	$ 15,885	$ 12,799	$ 47,025	$ 40,419

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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