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]	Convertible Note due 2024	Convertible Note due 2024 Additional Paid-in Capital [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member]	[1]	Cumulative Effect, Period of Adoption, Adjustment [Member] Retained Earnings [Member]	[1]	Cumulative Effect, Period of Adoption, Adjusted Balance [Member]	Cumulative Effect, Period of Adoption, Adjusted Balance [Member] Common Stock [Member]	Cumulative Effect, Period of Adoption, Adjusted Balance [Member] Additional Paid-in Capital [Member]	Cumulative Effect, Period of Adoption, Adjusted Balance [Member] Retained Earnings [Member]	Cumulative Effect, Period of Adoption, Adjusted Balance [Member] AOCI Attributable to Parent [Member]
Common Stock, Beginning at Dec. 31, 2018		87,057
Balance at Dec. 31, 2018	$ 228,250	$ 87	$ 2,296,795	$ (2,067,416)	$ (1,216)							$ 1,400		$ 1,400		$ 229,650	$ 87	$ 2,296,795	$ (2,066,016)	$ (1,216)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ (11,494)			(11,494)
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201807Member
Other comprehensive loss, net of tax	$ (4,153)				(4,153)
Issuance of common stock under option, stock award and purchase plans, Shares		3,258
Issuance of common stock under option, stock award and purchase plans, Value	4,295	$ 3	4,292
Stock-based compensation	8,843		8,843
Adjustments to Additional Paid in Capital, Warrant Issued	16,142		16,142
Conversion feature of Convertible Senior Notes										$ 24,878	$ 24,878
Portion of conversion feature of 4.00% Convertible Senior Notes due 2020 exchanged						$ 27,111	$ 27,111
Issuance of warrant, amount	16,142
Common Stock, Ending at Sep. 27, 2019		90,315
Balance at Sep. 27, 2019	241,050	$ 90	2,323,839	(2,077,510)	(5,369)
Common Stock, Beginning at Jun. 28, 2019		89,074
Balance at Jun. 28, 2019	212,066	$ 89	2,302,798	(2,089,167)	(1,654)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	11,657			11,657
Other comprehensive loss, net of tax	(3,715)				(3,715)
Issuance of common stock under option, stock award and purchase plans, Shares		1,241
Issuance of common stock under option, stock award and purchase plans, Value	2,976	$ 1	2,975
Stock-based compensation	4,157		4,157
Adjustments to Additional Paid in Capital, Warrant Issued	16,142		16,142
Conversion feature of Convertible Senior Notes										$ 24,878	$ 24,878
Portion of conversion feature of 4.00% Convertible Senior Notes due 2020 exchanged						(27,111)	(27,111)
Common Stock, Ending at Sep. 27, 2019		90,315
Balance at Sep. 27, 2019	241,050	$ 90	2,323,839	(2,077,510)	(5,369)
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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(42,736)			(42,736)
Other comprehensive loss, net of tax	3,462				3,462
Issuance of common stock under option, stock award and purchase plans, Shares		3,444
Issuance of common stock under option, stock award and purchase plans, Value	3,843	$ 4	3,839
Stock-based compensation	13,768		13,768
Adjustments to Additional Paid in Capital, Warrant Issued	0		(2)
Conversion feature of Convertible Senior Notes								$ 8,254	$ 8,254
Portion of conversion feature of 4.00% Convertible Senior Notes due 2020 exchanged						(6,909)	(6,909)
Issuance of warrant, shares		2,413
Issuance of warrant, amount		$ 2
Stock Redeemed or Called During Period, Value						2,329	2,329
Common Stock, Ending at Sep. 25, 2020		97,732
Balance at Sep. 25, 2020	234,457	$ 98	2,348,638	(2,114,676)	397
Common Stock, Beginning at Jun. 26, 2020		96,863
Balance at Jun. 26, 2020	230,282	$ 97	2,342,856	(2,109,295)	(3,376)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(5,381)			(5,381)
Other comprehensive loss, net of tax	3,773				3,773
Issuance of common stock under option, stock award and purchase plans, Shares		869
Issuance of common stock under option, stock award and purchase plans, Value	1,892	$ 1	1,891
Stock-based compensation	3,972		3,972
Portion of conversion feature of 4.00% Convertible Senior Notes due 2020 exchanged						$ (81)	$ (81)
Common Stock, Ending at Sep. 25, 2020		97,732
Balance at Sep. 25, 2020	$ 234,457	$ 98	$ 2,348,638	$ (2,114,676)	$ 397

[1] See Note 2, “Summary of Significant Accounting Policies - Recently Adopted Accounting Pronouncements” on Form 10-K for the year ended December 31, 2019 for more information on the adoption of Accounting Standard Update (“ASU”) No. 2018-07, Compensation-Stock Compensation (“Topic 718”): Improvements to Nonemployee Share-Based Payment Accounting issued by the Financial Accounting Standards Board.