Net Income (Loss) Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009	Dec. 31, 2011 Stock Options [Member]	Dec. 31, 2010 Stock Options [Member]	Dec. 31, 2011 Convertible Note [Member]	Dec. 31, 2011 Convertible Note Hedge And Warrant [Member]	Mar. 31, 2009 Convertible Note Hedge And Warrant [Member]
Net Income (Loss) Per Common Share [Line Items]
Income (loss) from continuing operations	$ 347,893		$ 374,602		$ (135,363)
Income from discontinued operations, net	1,545		5,128		1,526
Gain on disposal of discontinued operations	24,371
Net income (loss) for basic net income (loss) per share	373,809		379,730		(133,837)
Income impact of assumed conversion of convertible notes			13,203	[1]
Net income (loss) for diluted net income (loss) per share	$ 373,809		$ 392,933		$ (133,837)
Weighted average common shares-basic	184,683,000		179,924,000		173,604,000
Incremental shares from assumed conversion of convertible notes	21,504,000	[2]	30,848,000	[2]
Convertible note hedge warrant shares	16,224,000	[3]	10,492,000	[3]
Restricted stock units	3,773,000		5,001,000
Stock options	566,000		443,000
Employee stock purchase rights	70,000		99,000
Dilutive potential common shares	42,137,000		46,883,000
Weighted average commons shares-diluted	226,820,000		226,807,000		173,604,000
Net income (loss) per common shares-basic, Continuing operations	$ 1.88		$ 2.08		$ (0.78)
Net income (loss) per common shares-basic, Discontinued operations	$ 0.14		$ 0.03		$ 0.01
Net income (loss) per common shares-basic, Total	$ 2.02		$ 2.11		$ (0.77)
Net income (loss) per common shares-diluted, Continuing operations	$ 1.53		$ 1.71		$ (0.78)
Net income (loss) per common shares-diluted, Discontinued operations	$ 0.12		$ 0.02		$ 0.01
Net income (loss) per common shares-diluted, Total	$ 1.65		$ 1.73		$ (0.77)
Potential outstanding stock options to exercise, in shares						700,000	5,300,000
Initial debt conversion price	$ 5.48							$ 5.48	$ 7.67	$ 7.67
Shares that will be issued upon conversion	34,703,196		34,700,000

[1] Income impact of convertible notes for 2010 represents interest expense that would have not been recorded if the notes converted at the beginning of the period.

[2] Incremental shares from assumed conversion of the convertible notes for 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 will 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. For 2010, incremental shares from assumed conversion of the convertible notes represent the 34.7 million of shares that will be issued upon conversion.

[3] Convertible notes hedge warrant shares for 2011 and 2010 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 will 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. Teradyne's call option on its common stock (convertible note hedge transaction) is excluded from the calculation of diluted shares because the effect would be anti-dilutive. See Note G: "Debt" regarding convertible note hedge transaction.