Net Income Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended						3 Months Ended			3 Months Ended
	Apr. 01, 2012		Apr. 03, 2011		Apr. 03, 2011 Convertible Notes [Member]	Apr. 01, 2012 Convertible Notes [Member]	Apr. 03, 2011 Convertible Notes Hedge Warrant [Member]	Apr. 01, 2012 Convertible Notes Hedge Warrant [Member]	Mar. 31, 2009 Convertible Notes Hedge Warrant [Member]	Apr. 01, 2012 Stock Options [Member]	Apr. 03, 2011 Stock Options [Member]	Apr. 01, 2012 Restricted Stock Units [Member]
Net Income (Loss) Per Common Share [Line Items]
Income from continuing operations	$ 33,564		$ 69,938
Income from discontinued operations			1,703
Gain on disposal of discontinued operations			25,203
Net income for basic and diluted net income per share	$ 33,564		$ 96,844
Weighted average common shares-basic	185,838,000		184,720,000
Incremental shares from assumed conversion of convertible notes	23,000,000	[1]	23,360,000	[1]
Convertible notes hedge warrant shares	18,319,000	[2]	18,822,000	[2]
Restricted stock units	1,647,000		3,512,000
Stock options	2,325,000		1,605,000
Employee stock purchase rights	24,000		61,000
Dilutive potential common shares	45,315,000		47,360,000
Weighted average commons shares-diluted	231,153,000		232,080,000
Net income per common share-basic, Continuing operations	$ 0.18		$ 0.38
Net income per common share-basic, Discontinued operations			$ 0.14
Net income per common share-basic, Total	$ 0.18		$ 0.52
Net income per common share-diluted, Continuing operations	$ 0.15		$ 0.30
Net income per common share-diluted, Discontinued operations			$ 0.12
Net income per common share-diluted, Total	$ 0.15		$ 0.42
Computation of diluted net income per common excluding the effect of the potential exercise of stock options and restricted stock units										300,000	1,600,000	1,000,000
Initial debt conversion price	$ 5.48					$ 5.48		$ 7.67	$ 7.67
Shares that would be issued upon conversion	34,703,196				34,700,000		34,700,000

[1] Incremental shares from assumed conversion of the convertible notes for the three months ended April 1, 2012 and April 3, 2011 are calculated using the difference between the average Teradyne stock price for the period and the conversion price of $5.48, multiplied by the 34.7 million shares that would be issued upon conversion. The result of this calculation, representing total intrinsic value of the convertible debt, is divided by the average Teradyne stock price for the period.

[2] Convertible notes hedge warrant shares for the three months ended April 1, 2012 and April 3, 2011 are calculated using the difference between the average Teradyne stock price for the period and the warrant price of $7.67, multiplied by the 34.7 million shares that would be issued upon conversion. The result of this calculation, representing total intrinsic value of the warrant, is divided by the average Teradyne stock price for the period.