Restructuring Costs - Additional Information (Details) - USD ($) $ in Thousands		1 Months Ended		3 Months Ended		12 Months Ended			14 Months Ended
		Nov. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018
Restructuring Cost And Reserve [Line Items]
Restructuring costs	[1]					$ 3,525	$ 1,785	$ 25,256
Accrued Expenses And Other Current Liabilities
Restructuring Cost And Reserve [Line Items]
Balances recorded in accrued expenses and other current liabilities				$ 600	$ 1,000	600	1,000		$ 600
Other Non-Current Liabilities
Restructuring Cost And Reserve [Line Items]
Balances recorded in other non-current liabilities				300	400	300	400		300
Derecognition of Goodwill And Intangibles Assets
Restructuring Cost And Reserve [Line Items]
Restructuring costs						$ 0	$ 0	$ 15,895
November 2017 Restructuring Plan
Restructuring Cost And Reserve [Line Items]
Restructuring costs				$ 3,500	$ 1,700				$ 5,200
November 2016 Restructuring Plan
Restructuring Cost And Reserve [Line Items]
Restructuring costs		$ 1,500
November 2016 Restructuring Plan | Derecognition of Goodwill And Intangibles Assets
Restructuring Cost And Reserve [Line Items]
Restructuring costs		$ 15,900
March 2016 Restructuring Plan
Restructuring Cost And Reserve [Line Items]
Restructuring costs			$ 7,900

[1] Includes stock-based compensation, net of amounts capitalized as follows: Year Ended December 31, (in thousands) 2018 2017 2016 Cost of revenue $8,931 $2,503 $4,114 Research and development 48,739 9,918 5,756 Sales and marketing 19,046 8,069 8,712 General and administrative 55,054 14,496 12,301 Restructuring — — 2,074 Stock-based compensation, net of amounts capitalized $131,770 $34,986 $32,957