Goodwill and Other Intangible Assets - Schedule of Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Goodwill [Line Items]
Balance as of January 1	$ 686,108	$ 683,683
Effect of foreign currency translation	(2,574)	2,425
Balance as of December 31	715,644	$ 686,108
The Future Customer
Goodwill [Line Items]
Goodwill resulting from business combinations	7,597
DMS Disaster Consultants
Goodwill [Line Items]
Goodwill resulting from business combinations	10,121
Vista Limited
Goodwill [Line Items]
Goodwill resulting from business combinations	$ 14,392

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
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-Section 45
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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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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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