CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Convertible Note due 2020	Convertible Note due 2020 Additional Paid-in Capital [Member]	Convertible Note due 2022	Convertible Note due 2022 Additional Paid-in Capital [Member]
Common Stock, Beginning at Dec. 31, 2019		91,875
Balance at Dec. 31, 2019	$ 252,446	$ 92	$ 2,327,359	$ (2,071,940)	$ (3,065)
Net loss	(37,355)			(37,355)
Other comprehensive income (loss), net of tax	(311)				(311)
Issuance of common stock under stock option, award and purchase plans, Shares		2,575
Issuance of common stock under stock option, award and purchase plans, Value	1,951	$ 3	1,948
Stock-based compensation	9,796		9,796
Conversion feature of 2022 Notes	8,254		8,254
Conversion feature of exchanged portion of 2020 Notes	(6,909)		(6,909)
Exercise of warrant, shares		2,413
Excercise of warrant, amount		$ 2
Adjustments to Additional Paid in Capital, Warrant Excercised	0		(2)
Adjustment to APIC - Reclassification from Mezzanine Equity to Equity for Convertible Notes						$ 2,410	$ 2,410
Common Stock, Ending at Jun. 26, 2020		96,863
Balance at Jun. 26, 2020	230,282	$ 97	2,342,856	(2,109,295)	(3,376)
Common Stock, Beginning at Mar. 27, 2020		96,566
Balance at Mar. 27, 2020	236,322	$ 97	2,336,459	(2,093,894)	(6,340)
Net loss	(15,401)			(15,401)
Other comprehensive income (loss), net of tax	2,964				2,964
Issuance of common stock under stock option, award and purchase plans, Shares		297
Issuance of common stock under stock option, award and purchase plans, Value	(220)	$ 0	(220)
Stock-based compensation	3,495		3,495
Conversion feature of 2022 Notes	8,254		8,254
Conversion feature of exchanged portion of 2020 Notes	(6,909)		(6,909)
Adjustment to APIC - Reclassification from Mezzanine Equity to Equity for Convertible Notes						$ 1,777	$ 1,777
Common Stock, Ending at Jun. 26, 2020		96,863
Balance at Jun. 26, 2020	230,282	$ 97	2,342,856	(2,109,295)	(3,376)
Common Stock, Beginning at Dec. 31, 2020		98,204
Balance at Dec. 31, 2020	258,302	$ 98	2,353,559	(2,101,211)	5,856
Net loss	(8,133)			(8,133)
Other comprehensive income (loss), net of tax	(3,141)				(3,141)
Issuance of common stock under stock option, award and purchase plans, Shares		3,590
Issuance of common stock under stock option, award and purchase plans, Value	7,875	$ 4	7,871
Stock-based compensation	12,421		12,421
Common Stock, Ending at Jul. 02, 2021		101,794
Balance at Jul. 02, 2021	267,324	$ 102	2,373,851	(2,109,344)	2,715
Common Stock, Beginning at Apr. 02, 2021		100,993
Balance at Apr. 02, 2021	259,770	$ 101	2,365,129	(2,107,335)	1,875
Net loss	(2,009)			(2,009)
Other comprehensive income (loss), net of tax	840				840
Issuance of common stock under stock option, award and purchase plans, Shares		801
Issuance of common stock under stock option, award and purchase plans, Value	3,100	$ 1	3,099
Stock-based compensation	4,059		4,059
Adjustment to APIC - Reclassification from Mezzanine Equity to Equity for Convertible Notes								$ 1,564	$ 1,564
Common Stock, Ending at Jul. 02, 2021		101,794
Balance at Jul. 02, 2021	$ 267,324	$ 102	$ 2,373,851	$ (2,109,344)	$ 2,715