Computation of Basic and Diluted Net Income Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Jul. 01, 2018	Jul. 02, 2017	Jul. 01, 2018	Jul. 02, 2017
Net Income Loss Per Common Share
Net income for basic and diluted net income per share		$ 101,037	$ 174,976	$ 188,010	$ 260,197
Weighted average common shares-basic		190,730	198,774	192,992	199,390
Incremental shares from assumed conversion of convertible notes	[1]	2,643	752	3,520	376
Convertible note hedge warrant shares	[2]			915
Employee stock purchase plan		43	63	28	36
Dilutive potential common shares		4,179	2,755	6,205	2,342
Weighted average common shares-diluted		194,909	201,529	199,197	201,732
Net income per common share-basic		$ 0.53	$ 0.88	$ 0.97	$ 1.30
Net income per common share-diluted		$ 0.52	$ 0.87	$ 0.94	$ 1.29
Restricted Stock Units
Net Income Loss Per Common Share
Incremental shares attributable to share based payment arrangements		1,219	1,622	1,444	1,576
Stock Options
Net Income Loss Per Common Share
Incremental shares attributable to share based payment arrangements		274	318	298	354

[1] Incremental shares from assumed conversion of the convertible notes was calculated using the difference between the average Teradyne stock price for the period and the conversion price of $31.80, multiplied by 14.5 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 $39.91, multiplied by 14.5 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.