Recent Accounting Pronouncements - Revenue From Contracts With Customers, Financial Statement Impact (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 30, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue, Net	$ 90,127	$ 82,943
Cost of Goods and Services Sold	42,944	42,535
Gross Profit	47,183	40,408
Selling, general and administrative	31,163	34,631
Operating Income (Loss)	(9,327)	(21,158)
Loss before income taxes	(12,616)	(24,259)
Net loss	(13,694)	$ (24,027)
Accounts receivable, net	74,760			$ 69,844
Prepaid expenses and other current assets	29,967			18,931
Other long-term assets	43,647			42,913
Deferred revenue	57,629			52,429
Other non-current liabilities	21,273			22,626
Accumulated deficit	(2,060,075)			$ (2,057,812)
Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts receivable, net			$ 71,625
Prepaid expenses and other current assets			22,509
Other long-term assets			43,686
Deferred revenue			47,603
Other non-current liabilities			22,153
Accumulated deficit			(2,046,381)
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue, Net	89,323
Cost of Goods and Services Sold	42,825
Gross Profit	46,498
Selling, general and administrative	30,971
Operating Income (Loss)	(9,820)
Loss before income taxes	(13,109)
Net loss	(14,187)
Accounts receivable, net	72,358
Prepaid expenses and other current assets	24,321
Other long-term assets	43,040
Deferred revenue	60,569
Other non-current liabilities	21,602
Accumulated deficit	(2,071,999)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue, Net	804
Cost of Goods and Services Sold	119
Gross Profit	685
Selling, general and administrative	192
Operating Income (Loss)	493
Loss before income taxes	493
Net loss	493
Accounts receivable, net	2,402		1,781
Prepaid expenses and other current assets	5,646		3,578
Other long-term assets	607		773
Deferred revenue	(2,940)		(4,826)
Other non-current liabilities	(329)		(473)
Accumulated deficit	$ 11,924		$ 11,431