Recent Accounting Pronouncements - Narratives (Details) - USD ($)	3 Months Ended
	Mar. 30, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit	$ (2,060,075,000)			$ (2,057,812,000)
Revenue, Net	90,127,000	$ 82,943,000
Cost of Goods and Services Sold	42,944,000	42,535,000
Net Capitalized Contract Costs	7,149,000			4,440,000
Capitalized Contract Cost, Amortization	200,000
Deferred Revenue, Revenue Recognized	19,900,000
Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit			$ (2,046,381,000)
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	11,924,000		11,431,000
Revenue, Net	804,000
Cost of Goods and Services Sold	119,000
Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	0
Accounting Standards Update 2016-18 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Restricted Cash	300,000	$ 1,800,000		$ 1,700,000	$ 1,800,000
Prepaid Expenses and Other Current Assets [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Capitalized Contract Costs	800,000
Other Noncurrent Assets [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Capitalized Contract Costs	$ 500,000
Sales Commission Contract Costs [Member] | Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit			$ 1,400,000