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	(21,954)			(21,954)
Other comprehensive loss, net of tax	(3,275)				(3,275)
Issuance of common stock under stock option, award and purchase plans, Shares		2,278
Issuance of common stock under stock option, award and purchase plans, Value	2,171	$ 3	2,168
Stock-based compensation	6,301		6,301
Exercise of warrant, shares		2,413
Issuance of warrant, amount		$ 2
Adjustments to Additional Paid in Capital, Other exercise of warrant	0		(2)
Adjustment to APIC - Reclassification from Mezzanine Equity to Equity for 2020 Notes						$ 633	$ 633
Common Stock, Ending at Mar. 27, 2020		96,566
Balance at Mar. 27, 2020	236,322	$ 97	2,336,459	(2,093,894)	(6,340)
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	(6,124)			(6,124)
Other comprehensive loss, net of tax	(3,981)				(3,981)
Issuance of common stock under stock option, award and purchase plans, Shares		2,789
Issuance of common stock under stock option, award and purchase plans, Value	4,775	$ 3	4,772
Stock-based compensation	8,362		8,362
Adjustments to APIC - Reclassification from Equity to Mezzanine equity for 2022 Notes								$ (1,564)	$ (1,564)
Common Stock, Ending at Apr. 02, 2021		100,993
Balance at Apr. 02, 2021	$ 259,770	$ 101	$ 2,365,129	$ (2,107,335)	$ 1,875