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	310	$ 0	230	0	0	$ 80
Employee stock purchase plan (in shares)						(8)
Amortization of unrecognized stock-based compensation	4,057	0	4,057	0	0	$ 0
Foreign currency translation adjustments	739	0	0	739	0	0
Grant of restricted stock units to settle accrued bonus	7,643	0	7,643	0	0	0
Settlement of restricted stock units	(8,637)	0	(806)	0	(5,892)	$ (1,939)
Settlement of restricted stock units (in shares)						(463)
Unrealized gain (loss) on short-term investments	(40)	0	0	(40)	0	$ 0
Dividends and dividend equivalent rights	(6,875)	0	585	0	(7,460)	0
Net income	20,340	0	0	0	20,340	0
Balance at Mar. 30, 2018	306,625	$ 66	221,939	(1,330)	310,978	$ (225,028)
Balances (in shares) at Mar. 30, 2018		65,707				13,698
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	(629)
Unrealized gain (loss) on short-term investments	(21)
Net income	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 Mar. 30, 2018	306,625	$ 66	221,939	(1,330)	310,978	$ (225,028)
Balances (in shares) at Mar. 30, 2018		65,707				13,698
Employee stock purchase plan	382	$ 0	302	0	0	$ 80
Employee stock purchase plan (in shares)						(8)
Amortization of unrecognized stock-based compensation	1,576	0	1,576	0	0	$ 0
Foreign currency translation adjustments	(1,368)	0	0	(1,368)	0	0
Settlement of restricted stock units	0	0	(194)	0	0	$ 194
Settlement of restricted stock units (in shares)						(21)
Unrealized gain (loss) on short-term investments	19	0	0	19	0	$ 0
Dividends and dividend equivalent rights	(6,893)	0	73	0	(6,966)	0
Net income	18,425	0	0	0	18,425	0
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. 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	372	$ 0	302	0	0	$ 70
Employee stock purchase plan (in shares)						(7)
Amortization of unrecognized stock-based compensation	3,663	0	3,663	0	0	$ 0
Foreign currency translation adjustments	117	0	0	117	0	0
Grant of restricted stock units to settle accrued bonus	7,947	0	7,947	0	0	0
Settlement of restricted stock units	(11,194)	0	(860)	0	(5,146)	$ (5,188)
Settlement of restricted stock units (in shares)						(395)
Unrealized gain (loss) on short-term investments	154	0	0	154	0	$ 0
Dividends and dividend equivalent rights	(8,503)	0	581	0	(9,084)	0
Net income	22,712	0	0	0	22,712	0
Balance at Mar. 29, 2019	329,177	$ 66	238,916	(2,582)	350,506	$ (257,729)
Balances (in shares) at Mar. 29, 2019		65,707				13,806
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	(124)
Unrealized gain (loss) on short-term investments	403
Net income	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 Mar. 29, 2019	329,177	$ 66	238,916	(2,582)	350,506	$ (257,729)
Balances (in shares) at Mar. 29, 2019		65,707				13,806
Employee stock purchase plan	473	$ 0	385	0	0	$ 88
Employee stock purchase plan (in shares)						(8)
Amortization of unrecognized stock-based compensation	1,685	0	1,685	0	0	$ 0
Foreign currency translation adjustments	(241)	0	0	(241)	0	0
Settlement of restricted stock units	11	0	(101)	0	0	$ 112
Settlement of restricted stock units (in shares)						(10)
Unrealized gain (loss) on short-term investments	249	0	0	249	0	$ 0
Dividends and dividend equivalent rights	(8,496)	0	45	0	(8,541)	0
Net income	20,994	0	0	0	20,994	0
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