Summary of Significant Accounting Policies - Revenue from Contracts with Customers Beginning Balance Sheet Impact (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net		$ 81,795		$ 69,844
Prepaid expenses and other current assets		23,280		18,931
Other long-term assets		38,377		42,913
Deferred revenue		41,592		52,429
Other non-current liabilities		18,228		22,626
Accumulated deficit		(2,067,416)		(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
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		1,841	1,781
Prepaid expenses and other current assets		4,213	3,578
Other long-term assets		505	773
Deferred revenue		(5,525)	(4,826)
Other non-current liabilities		(306)	(473)
Accumulated deficit		12,390
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		79,954
Prepaid expenses and other current assets		19,067
Other long-term assets		37,872
Deferred revenue		47,117
Other non-current liabilities		18,534
Accumulated deficit		(2,079,806)
Retained Earnings [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accumulated deficit		$ (2,067,416)		$ (2,057,812)
Retained Earnings [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accumulated deficit			(2,046,381)
Retained Earnings [Member] | 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]
Accumulated deficit	[1]		$ 11,431

[1] See Note 2, “Summary of Significant Accounting Policies-Recently Adopted Accounting Pronouncements,” for more information on the adoption of ASC 606, Revenue from Contracts with Customers (“Topic 606”) issued by the Financial Accounting Standards Board.