Computation of Basic and Diluted Net (Loss) Income Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 29, 2019	Sep. 30, 2018	Sep. 29, 2019	Sep. 30, 2018
Net Income Loss Per Common Share
Net income for basic and diluted net income per share		$ 135,860	$ 119,981	$ 342,395	$ 307,991
Weighted average common shares-basic		169,641	185,744	171,471	190,576
Incremental shares from assumed conversion of convertible notes	[1]	5,800	3,025	4,117	3,356
Convertible note hedge warrant shares	[2]	3,580	108	1,786	646
Employee stock purchase plan		5	22	13	26
Dilutive potential common shares		10,853	4,761	7,214	5,724
Weighted average common shares-diluted		180,494	190,505	178,685	196,300
Net income per common share-basic		$ 0.80	$ 0.65	$ 2.00	$ 1.62
Net income per common share-diluted		$ 0.75	$ 0.63	$ 1.92	$ 1.57
Restricted Stock Units
Net Income Loss Per Common Share
Incremental shares attributable to share based payment arrangements		1,313	1,331	1,112	1,406
Stock Options
Net Income Loss Per Common Share
Incremental shares attributable to share based payment arrangements		155	275	186	290

[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 $31.70, 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 note hedge warrant shares were calculated using the difference between the average Teradyne stock price for the period and the warrant price of $39.78, 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.