Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional paid-in capital [Member]	Accumulated other comprehensive income (loss) [Member]	Retained earnings [Member]	Treasury Stock [Member]
Balance at Dec. 29, 2017	$ 289,088	$ 66	$ 210,230	$ (2,029)	$ 303,990	$ (223,169)
Balances (in shares) at Dec. 29, 2017		65,707				14,169
Employee stock purchase plan	692		532			$ 160
Employee stock purchase plan (in shares)						(16)
Amortization of unrecognized stock-based compensation	5,633		5,633
Foreign currency translation adjustments	(629)			(629)
Grant of restricted stock units to settle accrued bonus	7,643		7,643
Settlement of restricted stock units	(8,637)		(1,000)		(5,892)	$ (1,745)
Settlement of restricted stock units (in shares)						(484)
Unrealized gain (loss) on short-term investments	(21)			(21)
Dividends and dividend equivalent rights	(13,768)		658		(14,426)
Net income	38,765				38,765
Balance at Jun. 29, 2018	318,766	$ 66	223,696	(2,679)	322,437	$ (224,754)
Balances (in shares) at Jun. 29, 2018		65,707				13,669
Balance at Dec. 29, 2017	289,088	$ 66	210,230	(2,029)	303,990	$ (223,169)
Balances (in shares) at Dec. 29, 2017		65,707				14,169
Foreign currency translation adjustments	(933)
Unrealized gain (loss) on short-term investments	(52)
Net income	56,218
Balance at Sep. 28, 2018	330,634	$ 66	225,454	(3,014)	332,907	$ (224,779)
Balances (in shares) at Sep. 28, 2018		65,707				13,655
Balance at Jun. 29, 2018	318,766	$ 66	223,696	(2,679)	322,437	$ (224,754)
Balances (in shares) at Jun. 29, 2018		65,707				13,669
Employee stock purchase plan	373		303			$ 70
Employee stock purchase plan (in shares)						(7)
Amortization of unrecognized stock-based compensation	1,488		1,488
Foreign currency translation adjustments	(304)			(304)
Settlement of restricted stock units	(202)		(107)			$ (95)
Settlement of restricted stock units (in shares)						(7)
Unrealized gain (loss) on short-term investments	(31)			(31)
Dividends and dividend equivalent rights	(6,909)		74		(6,983)
Net income	17,453				17,453
Balance at Sep. 28, 2018	330,634	$ 66	225,454	(3,014)	332,907	$ (224,779)
Balances (in shares) at Sep. 28, 2018		65,707				13,655
Balance at Dec. 28, 2018	313,909	$ 66	227,283	(2,853)	342,024	$ (252,611)
Balances (in shares) at Dec. 28, 2018		65,707				14,208
Employee stock purchase plan	845		687			$ 158
Employee stock purchase plan (in shares)						(15)
Amortization of unrecognized stock-based compensation	5,348		5,348
Foreign currency translation adjustments	(124)			(124)
Grant of restricted stock units to settle accrued bonus	7,947		7,947
Settlement of restricted stock units	(11,183)		(961)		(5,146)	$ (5,076)
Settlement of restricted stock units (in shares)						(405)
Unrealized gain (loss) on short-term investments	403			403
Dividends and dividend equivalent rights	(16,999)		626		(17,625)
Net income	43,706				43,706
Balance at Jun. 28, 2019	343,852	$ 66	240,930	(2,574)	362,959	$ (257,529)
Balances (in shares) at Jun. 28, 2019		65,707				13,788
Balance at Dec. 28, 2018	313,909	$ 66	227,283	(2,853)	342,024	$ (252,611)
Balances (in shares) at Dec. 28, 2018		65,707				14,208
Foreign currency translation adjustments	(657)
Unrealized gain (loss) on short-term investments	373
Net income	63,339
Balance at Sep. 27, 2019	357,279	$ 66	242,756	(3,137)	374,033	$ (256,439)
Balances (in shares) at Sep. 27, 2019		65,707				13,682
Balance at Jun. 28, 2019	343,852	$ 66	240,930	(2,574)	362,959	$ (257,529)
Balances (in shares) at Jun. 28, 2019		65,707				13,788
Employee stock purchase plan	389		328			$ 61
Employee stock purchase plan (in shares)						(6)
Exercise of stock options	735		(294)			$ 1,029
Exercise of stock options (in shares)						(100)
Amortization of unrecognized stock-based compensation	1,748		1,748
Foreign currency translation adjustments	(533)			(533)
Unrealized gain (loss) on short-term investments	(30)			(30)
Dividends and dividend equivalent rights	(8,515)		44		(8,559)
Net income	19,633				19,633
Balance at Sep. 27, 2019	$ 357,279	$ 66	$ 242,756	$ (3,137)	$ 374,033	$ (256,439)
Balances (in shares) at Sep. 27, 2019		65,707				13,682