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
		Oct. 04, 2015	Sep. 28, 2014	Oct. 04, 2015	Sep. 28, 2014
Net Income Loss Per Common Share
Net income for basic and diluted net income per share		$ 71,453	$ 82,949	$ 207,118	$ 185,083
Weighted average common shares-basic		210,032	207,381	213,688	198,367
Incremental shares from assumed conversion of convertible notes	[1]				6,684
Convertible note hedge warrant shares	[2]		8,885		16,744
Employee stock purchase plan		23	21	40	28
Dilutive potential common shares		1,704	10,952	1,660	25,428
Weighted average common shares-diluted		211,736	218,333	215,348	223,795
Net income per common share-basic		$ 0.34	$ 0.40	$ 0.97	$ 0.93
Net income per common share-diluted		$ 0.34	$ 0.38	$ 0.96	$ 0.83
Restricted Stock Units
Net Income Loss Per Common Share
Incremental shares attributable to share based payment arrangements		1,103	1,167	994	975
Stock Options
Net Income Loss Per Common Share
Incremental shares attributable to share based payment arrangements		578	879	626	997

[1] Incremental shares from the 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 $5.48, multiplied by 34.7 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 $7.6650, multiplied by 34.7 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. Teradyne's call option on its common stock (convertible note hedge transaction) was excluded from the calculation of diluted shares because the effect was anti-dilutive. See Note F: "Debt" regarding the convertible note hedge transaction.