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Operating Segments and Enterprise-Wide Information - Operating Results by Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 25, 2021	Sep. 26, 2020	Sep. 25, 2021	Sep. 26, 2020
Segment Reporting Information [Line Items]
Revenues	$ 189,964	$ 177,996	$ 564,676	$ 496,573
Gross profit	$ 80,219	$ 76,749	$ 233,208	$ 210,306
Gross margin	42.20%	43.10%	41.30%	42.40%
Probe Cards
Segment Reporting Information [Line Items]
Revenues	$ 154,850	$ 150,773	$ 467,389	$ 419,272
Systems
Segment Reporting Information [Line Items]
Revenues	35,114	27,223	97,287	77,301
Operating segments | Probe Cards
Segment Reporting Information [Line Items]
Revenues	154,850	150,773	467,389	419,272
Gross profit	$ 69,868	$ 69,641	$ 206,783	$ 191,907
Gross margin	45.10%	46.20%	44.20%	45.80%
Operating segments | Systems
Segment Reporting Information [Line Items]
Revenues	$ 35,114	$ 27,223	$ 97,287	$ 77,301
Gross profit	$ 17,553	$ 13,565	$ 48,059	$ 37,618
Gross margin	50.00%	49.80%	49.40%	48.70%
Operating segments | Corporate and Other
Segment Reporting Information [Line Items]
Revenues	$ 0	$ 0	$ 0	$ 0
Gross profit	$ (7,202)	$ (6,457)	$ (21,634)	$ (19,219)
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