Net Income Per Common Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Oct. 02, 2011		Sep. 30, 2012		Oct. 02, 2011
Net Income Loss Per Common Share
Income from continuing operations	$ 88,641		$ 56,706		$ 233,592		$ 214,728
Income from discontinued operations							1,703
Gain on disposal of discontinued operations							24,371
Net income for basic net income per share	$ 88,641		$ 56,706		$ 233,592		$ 240,802
Weighted average common shares-basic	187,364		185,102		186,592		185,063
Incremental shares from assumed conversion of convertible Note	21,890	[1]	19,540	[1]	22,397	[1]	21,870	[1]
Convertible note hedge warrant shares	16,765	[2]	13,475	[2]	17,474	[2]	16,737	[2]
Restricted stock units	1,423		3,377		1,413		3,942
Stock options	1,735		346		2,075		454
Employee stock purchase rights	33		52		52		75
Dilutive potential common shares	41,846		36,790		43,411		43,078
Weighted average common shares-diluted	229,210		221,892		230,003		228,141
Net income per common share-basic, Continuing operations	$ 0.47		$ 0.31		$ 1.25		$ 1.16
Net income per common share-basic, Discontinued operations							$ 0.14
Net income per common share-basic, Total	$ 0.47		$ 0.31		$ 1.25		$ 1.30
Net income per common share-diluted, Continuing operations	$ 0.39		$ 0.26		$ 1.02		$ 0.94
Net income per common share-diluted, Discontinued operations							$ 0.12
Net income per common share-diluted, Total	$ 0.39		$ 0.26		$ 1.02		$ 1.06

[1] Incremental shares from assumed conversion of the convertible notes for the three and nine months ended September 30, 2012 and October 2, 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 the total intrinsic value of the convertible debt, is divided by the average Teradyne stock price for the period.

[2] Convertible note hedge warrant shares for the three and nine months ended September 30, 2012 and October 2, 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 the total intrinsic value of the warrant, is divided by the average Teradyne stock price for the period.