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Goodwill and Intangible Assets - Changes in Goodwill by Reporting Unit (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Goodwill [Line Items]
Opening balance	$ 1,574,466	$ 1,393,832
Goodwill relating to acquisitions consummated during the period		185,381
Impact of measurement period adjustments		(988)
Effect of exchange rate fluctuations	(19,787)	(3,759)
Closing balance	1,554,679	1,574,466
BCMI
Goodwill [Line Items]
Opening balance	417,213	398,601
Goodwill relating to acquisitions consummated during the period		20,072
Impact of measurement period adjustments		(380)
Effect of exchange rate fluctuations	(5,683)	(1,080)
Closing balance	411,530	417,213
CGRLH
Goodwill [Line Items]
Opening balance	555,130	512,296
Goodwill relating to acquisitions consummated during the period		44,365
Impact of measurement period adjustments		(151)
Effect of exchange rate fluctuations	(7,262)	(1,380)
Closing balance	547,868	555,130
HMS
Goodwill [Line Items]
Opening balance	602,123	482,935
Goodwill relating to acquisitions consummated during the period		120,944
Impact of measurement period adjustments		(457)
Effect of exchange rate fluctuations	(6,842)	(1,299)
Closing balance	$ 595,281	$ 602,123

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