Computation of Basic and Diluted Net Income Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended
		Apr. 04, 2021	Mar. 29, 2020
Net Income Loss Per Common Share
Net income for basic and diluted net income per share		$ 205,512	$ 176,191
Weighted average common shares-basic		166,491	166,589
Incremental shares from assumed conversion of convertible notes	[1]	10,310	7,333
Convertible note hedge warrant shares	[2]	9,429	5,492
Employee stock purchase plan		7	25
Dilutive potential common shares		21,249	14,147
Weighted average common shares-diluted		187,740	180,736
Net income per common share-basic		$ 1.23	$ 1.06
Net income per common share-diluted		$ 1.09	$ 0.97
Restricted Stock Units
Net Income Loss Per Common Share
Incremental shares attributable to share based payment arrangements		1,395	1,163
Stock Options
Net Income Loss Per Common Share
Incremental shares attributable to share based payment arrangements		108	134

[1] Incremental shares from assumed conversion of the convertible notes were calculated using the difference between the average Teradyne stock price for the period and the conversion price of $31.55, multiplied by 13.8 million shares. The result of this calculation, representing the total intrinsic value of the convertible debt, was divided by the average Teradyne stock price for the period.

[2] Convertible notes hedge warrant shares were calculated using the difference between the average Teradyne stock price for the period and the warrant price of $39.59, multiplied by 13.8 million shares. The result of this calculation, representing the total intrinsic value of the warrant, was divided by the average Teradyne stock price for the period.