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 2024
Common Stock, Beginning at Dec. 31, 2017			82,554
Balance at Dec. 31, 2017		$ 218,343	$ 83	$ 2,272,690	$ (2,057,812)	$ 3,382
Cumulative effect to retained earnings related to adoption of Topic 718 | Accounting Standards Update 2014-09 [Member]		11,431			11,431
Common Stock, Ending at Jan. 01, 2018			82,554
Balance at Jan. 01, 2018		229,774	$ 83	2,272,690	(2,046,381)	3,382
Common Stock, Beginning at Dec. 31, 2017			82,554
Balance at Dec. 31, 2017		218,343	$ 83	2,272,690	(2,057,812)	3,382
Net income (loss)		(24,365)			(24,365)
Other comprehensive loss, net of tax		(2,868)				(2,868)
Issuance of common stock under option, stock award and purchase plans, Shares			4,133
Issuance of common stock under option, stock award and purchase plans, Value		4,134	$ 4	4,130
Stock-based compensation		14,059		14,059
Issuance of warrant		2,295		2,295
Common Stock, Ending at Sep. 28, 2018			86,687
Balance at Sep. 28, 2018		223,029	$ 87	2,293,174	(2,070,746)	514
Common Stock, Beginning at Jun. 29, 2018			85,439
Balance at Jun. 29, 2018		220,735	$ 85	2,283,649	(2,062,988)	(11)
Net income (loss)		(7,758)			(7,758)
Other comprehensive loss, net of tax		525				525
Issuance of common stock under option, stock award and purchase plans, Shares			1,248
Issuance of common stock under option, stock award and purchase plans, Value		1,821	$ 2	1,819
Stock-based compensation		5,411		5,411
Issuance of warrant		2,295		2,295
Common Stock, Ending at Sep. 28, 2018			86,687
Balance at Sep. 28, 2018		223,029	$ 87	2,293,174	(2,070,746)	514
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 2016-09 [Member]	[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 income (loss)		(11,494)
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
Issuance of warrant		16,142		16,142
Portion of repurchase price recorded in additional paid-in capital in connection with partial repurchase of convertible notes due 2020		(27,111)		(27,111)
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt		24,878		24,878
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)
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
Issuance of warrant		16,142		16,142
Portion of repurchase price recorded in additional paid-in capital in connection with partial repurchase of convertible notes due 2020		(27,111)		(27,111)
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt		24,878		24,878
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)
Debt Instrument, Interest Rate, Stated Percentage							4.00%	2.00%

[1] See Note 2, “Recent Accounting Pronouncements” 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.