Recent Accounting Pronouncements - Narratives (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 29, 2018	Jun. 29, 2018	Jan. 01, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Revenue, Revenue Recognized	$ 24,100	$ 44,000
Accumulated deficit	(2,062,988)	(2,062,988)		$ (2,057,812)
Net Capitalized Contract Costs	1,800	1,800
Capitalized Contract Cost, Amortization	300	500
Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit			$ (2,046,381)
Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit	12,711	12,711	11,431
Accounting Standards Update 2016-18 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Restricted Cash	300	300		$ 1,700	$ 1,900	$ 1,800
Prepaid Expenses and Other Current Assets [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Capitalized Contract Costs	1,300	1,300
Other Noncurrent Assets [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Capitalized Contract Costs	$ 500	$ 500
Sales Commission Contract Costs [Member] | Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit			$ 1,400