Recent Accounting Pronouncements - Revenue From Contracts With Customers Beginning Balance Sheet Impact (Details) - USD ($) $ in Thousands	Jun. 29, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	$ 82,635		$ 69,844
Prepaid expenses and other current assets	19,377		18,931
Other long-term assets	42,863		42,913
Deferred revenue	56,278		52,429
Other non-current liabilities	19,169		22,626
Accumulated deficit	(2,062,988)		$ (2,057,812)
Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [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]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	78,065
Prepaid expenses and other current assets	15,918
Other long-term assets	42,360
Deferred revenue	60,032
Other non-current liabilities	19,594
Accumulated deficit	(2,075,699)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	4,570	1,781
Prepaid expenses and other current assets	3,459	3,578
Other long-term assets	503	773
Deferred revenue	(3,754)	(4,826)
Other non-current liabilities	(425)	(473)
Accumulated deficit	$ 12,711	$ 11,431