Computation of Basic and Diluted Net Income Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Oct. 01, 2017	Sep. 30, 2018	Oct. 01, 2017
Net Income Loss Per Common Share
Net income for basic and diluted net income per share		$ 119,981	$ 103,420	$ 307,991	$ 363,616
Weighted average common shares-basic		185,744	197,485	190,576	198,755
Incremental shares from assumed conversion of convertible notes	[1]	3,025	1,144	3,356	632
Convertible note hedge warrant shares	[2]	108		646
Employee stock purchase plan		22	8	26	26
Dilutive potential common shares		4,761	3,290	5,724	2,658
Weighted average common shares-diluted		190,505	200,775	196,300	201,413
Net income per common share-basic		$ 0.65	$ 0.52	$ 1.62	$ 1.83
Net income per common share-diluted		$ 0.63	$ 0.52	$ 1.57	$ 1.81
Restricted Stock Units
Net Income Loss Per Common Share
Incremental shares attributable to share based payment arrangements		1,331	1,832	1,406	1,663
Stock Options
Net Income Loss Per Common Share
Incremental shares attributable to share based payment arrangements		275	306	290	337

[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.