CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total		Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive (Loss) Income	Accumulated Deficit
Balance at Dec. 31, 2016	$ 1,828,659		$ 24,897	$ 1,593,684	$ (20,214)	$ 230,292
Balance, Shares at Dec. 31, 2016			199,177
Net issuance of common stock under stock-based plans	11,024		$ 277	10,747
Net issuance of common stock under stock-based plans (in shares)			2,211
Stock-based compensation expense	33,982			33,982
Repurchase of common stock	(200,304)		$ (730)			(199,574)
Repurchase of common stock (in shares)			(5,840)
Tax benefit related to stock options and restricted stock units	39,081					39,081
Cash dividends	(55,478)					(55,478)
Net income	257,692					257,692
Other comprehensive loss	38,990				38,990
Balance at Dec. 31, 2017	1,953,646		$ 24,444	1,638,413	18,776	272,013
Balance, Shares at Dec. 31, 2017			195,548
Net issuance of common stock under stock-based plans	129		$ 201	(72)
Net issuance of common stock under stock-based plans (in shares)			1,613
Stock-based compensation expense	33,304			33,304
Repurchase of common stock	(832,356)		$ (2,705)			(829,651)
Repurchase of common stock (in shares)			(21,639)
Cash dividends	(67,367)					(67,367)
Net income	451,779					451,779
Other comprehensive loss	(29,460)				(29,460)
Reclassification of unrealized gains on equity securities					(3,125)	3,125
Reclassification of tax effects resulting from the Tax Reform Act	769	[1]			769	(769)
Balance at Dec. 31, 2018	1,522,354		$ 21,940	1,671,645	(13,040)	(158,191)
Balance, Shares at Dec. 31, 2018			175,522
Cumulative effect of changes in accounting principle related to revenue recognition	12,679					12,679
Net issuance of common stock under stock-based plans	10,622		$ 223	10,399
Net issuance of common stock under stock-based plans (in shares)			1,784
Stock-based compensation expense	38,085			38,085
Repurchase of common stock	(491,202)		$ (1,362)			(489,840)
Repurchase of common stock (in shares)			(10,896)
Cash dividends	(61,355)					(61,355)
Net income	467,468					467,468
Other comprehensive loss	(5,814)				(5,814)
Balance at Dec. 31, 2019	$ 1,480,158		$ 20,801	$ 1,720,129	$ (18,854)	$ (241,918)
Balance, Shares at Dec. 31, 2019			166,410

[1] In the year ended December 31, 2018, Teradyne early adopted ASU 2018-02, “Income Statement—Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income.” As a result, the stranded tax effects resulting from the Tax Reform Act enacted in December 2017 were reclassified from accumulated other comprehensive income to retained earnings.