Goodwill and Acquired Intangible Assets - Schedule of the Changes in the Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Changes in the carrying amount of goodwill
Beginning balance	$ 1,498,688	$ 1,228,503
Measurement period adjustments	(6,667)	4,217
Foreign currency translation	(4,617)	10,546
Ending balance	1,487,404	1,498,688
Soasta, Inc.
Changes in the carrying amount of goodwill
Acquisitions	0	121,668
Nominum, Inc.
Changes in the carrying amount of goodwill
Acquisitions	$ 0	$ 133,754

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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