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 2022
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)
Cumulative effect to retained earnings related to adoption of Topic 718 | Accounting Standards Update 2018-07	[1]	1,400			1,400
Common Stock, Ending at Jan. 01, 2019			87,057
Balance at Jan. 01, 2019		229,650	$ 87	2,296,795	(2,066,016)	(1,216)
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)
Net loss		(23,151)			(23,151)
Other comprehensive loss, net of tax		(438)				(438)
Issuance of common stock under option, stock award and purchase plans, Shares			2,017
Issuance of common stock under option, stock award and purchase plans, Value		1,319	$ 2	1,317
Stock-based compensation		4,686		4,686
Common Stock, Ending at Jun. 28, 2019			89,074
Balance at Jun. 28, 2019		212,066	$ 89	2,302,798	(2,089,167)	(1,654)
Common Stock, Beginning at Mar. 29, 2019			88,784
Balance at Mar. 29, 2019		220,561	$ 89	2,300,259	(2,077,322)	(2,465)
Net loss		(11,845)			(11,845)
Other comprehensive loss, net of tax		811				811
Issuance of common stock under option, stock award and purchase plans, Shares			290
Issuance of common stock under option, stock award and purchase plans, Value			$ 0
Restricted Stock, Value, Shares Issued Net of Tax Withholdings		(36)		(36)
Stock-based compensation		2,575		2,575
Common Stock, Ending at Jun. 28, 2019			89,074
Balance at Jun. 28, 2019		212,066	$ 89	2,302,798	(2,089,167)	(1,654)
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 loss, net of tax		(311)				(311)
Issuance of common stock under option, stock award and purchase plans, Shares			2,575
Issuance of common stock under option, stock award and purchase plans, Value		1,951	$ 3	1,948
Stock-based compensation		9,796		9,796
Conversion feature of 4.375% Convertible Senior Notes due 2022		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
Adjustments to Additional Paid in Capital, Warrant Issued		0		(2)
Reclassification from mezzanine equity to equity for 4.00% Convertible Senior Notes due in 2020		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 loss, net of tax		2,964				2,964
Issuance of common stock under option, stock award and purchase plans, Shares			297
Issuance of common stock under option, stock award and purchase plans, Value			$ 0
Restricted Stock, Value, Shares Issued Net of Tax Withholdings		(220)		(220)
Stock-based compensation		3,495		3,495
Conversion feature of 4.375% Convertible Senior Notes due 2022		8,254		8,254
Portion of conversion feature of 4.00% Convertible Senior Notes due 2020 exchanged		(6,909)		(6,909)
Reclassification from mezzanine equity to equity for 4.00% Convertible Senior Notes due in 2020		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)
Debt Instrument, Interest Rate, Stated Percentage							4.00%	4.375%

[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.