Goodwill - Schedule of Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands		9 Months Ended
Jan. 31, 2020	Sep. 30, 2020
Goodwill [Line Items]
Balance as of December 31, 2019		$ 719,934
Effect of foreign currency translation		(1,188)
Balance as of September 30, 2020		906,999
ITG
Goodwill [Line Items]
Goodwill resulting from business combinations	$ 188,300	$ 188,253

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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