Consolidated Statement of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning Balance (in shares) at Dec. 31, 2018		170,820
Beginning Balance at Dec. 31, 2018	$ 1,135,263	$ 342	$ 529,208	$ 646,214	$ (40,501)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under stock plans (in shares)		1,475
Issuance of common stock under stock plans	31,780	$ 3	31,777
Repurchase of common stock (in shares)		(1,398)
Repurchase of common stock	(61,690)	$ (3)		(61,687)
Stock-based compensation expense	33,442		33,442
Payment of dividends	(25,682)			(25,682)
Net income	123,538			123,538
Net unrealized gain (loss) on available-for-sale investments, net of tax	4,827				4,827
Reclassification of credit (recovery) loss on investments	0
Reclassification of net realized (gain) loss on the sale of available-for-sale investments	(716)				(716)
Foreign currency translation adjustment	(1,544)				(1,544)
Ending Balance (in shares) at Sep. 29, 2019		170,897
Ending Balance at Sep. 29, 2019	1,239,218	$ 342	594,427	682,383	(37,934)
Beginning Balance (in shares) at Jun. 30, 2019		170,661
Beginning Balance at Jun. 30, 2019	1,191,640	$ 341	578,871	649,234	(36,806)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under stock plans (in shares)		236
Issuance of common stock under stock plans	5,363	$ 1	5,362
Repurchase of common stock (in shares)		0
Repurchase of common stock	0	$ 0		0
Stock-based compensation expense	10,194		10,194
Payment of dividends	(8,536)			(8,536)
Net income	41,685			41,685
Net unrealized gain (loss) on available-for-sale investments, net of tax	265				265
Reclassification of credit (recovery) loss on investments	0
Reclassification of net realized (gain) loss on the sale of available-for-sale investments	(294)				(294)
Foreign currency translation adjustment	(1,099)				(1,099)
Ending Balance (in shares) at Sep. 29, 2019		170,897
Ending Balance at Sep. 29, 2019	$ 1,239,218	$ 342	594,427	682,383	(37,934)
Beginning Balance (in shares) at Dec. 31, 2019	172,440	172,440
Beginning Balance at Dec. 31, 2019	$ 1,355,710	$ 345	639,372	753,268	(37,275)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under stock plans (in shares)		3,408
Issuance of common stock under stock plans	91,390	$ 6	91,384
Repurchase of common stock (in shares)		(1,215)
Repurchase of common stock	(51,036)	$ (2)		(51,034)
Stock-based compensation expense	32,076		32,076
Payment of dividends	(28,554)			(28,554)
Net income	106,841			106,841
Net unrealized gain (loss) on available-for-sale investments, net of tax	6,282				6,282
Reclassification of credit (recovery) loss on investments	(75)
Reclassification of net realized (gain) loss on the sale of available-for-sale investments	(3,591)				(3,591)
Foreign currency translation adjustment	$ (3,364)				(3,364)
Ending Balance (in shares) at Sep. 27, 2020	174,663	174,633
Ending Balance at Sep. 27, 2020	$ 1,505,829	$ 349	762,832	780,521	(37,873)
Beginning Balance (in shares) at Jun. 28, 2020		173,047
Beginning Balance at Jun. 28, 2020	1,376,478	$ 346	710,412	702,597	(36,877)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under stock plans (in shares)		1,586
Issuance of common stock under stock plans	43,155	$ 3	43,152
Repurchase of common stock (in shares)		0
Repurchase of common stock	0	$ 0		0
Stock-based compensation expense	9,268		9,268
Payment of dividends	(9,582)			(9,582)
Net income	87,506			87,506
Net unrealized gain (loss) on available-for-sale investments, net of tax	(2,308)				(2,308)
Reclassification of credit (recovery) loss on investments	0
Reclassification of net realized (gain) loss on the sale of available-for-sale investments	(786)				(786)
Foreign currency translation adjustment	$ 2,098				2,098
Ending Balance (in shares) at Sep. 27, 2020	174,663	174,633
Ending Balance at Sep. 27, 2020	$ 1,505,829	$ 349	$ 762,832	$ 780,521	$ (37,873)