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Business acquisitions - Hoodoo Digital, LLC. - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Payment for business acquisitions, net of cash acquired	$ 72,025	$ 186,633	$ 252,276
Goodwill	1,731,027	1,695,688	1,574,466
Acquisition related cost	$ 1,177	$ 2,650	$ 8,352
Hoodoo Digital, LLC
Business Acquisition [Line Items]
Ownership percentage acquired (in percentage)	100.00%
Purchase consideration	$ 66,592
Payment for business acquisitions, net of cash acquired	64,310
Cash and cash equivalents	2,283
Cash consideration to acquired certain assets and assumed certain liabilities	67,695
Consideration receivable	$ 1,102
Acquired intangible assets, weighted average amortization period	5 years
Goodwill	$ 44,216
Acquisition related cost	1,177
Acquired assets	5,629
Liabilities assumed	1,852
Indemnification assets	278
Hoodoo Digital, LLC \| BCMI
Business Acquisition [Line Items]
Goodwill	4,167
Hoodoo Digital, LLC \| CGRLH
Business Acquisition [Line Items]
Goodwill	7,032
Hoodoo Digital, LLC \| HMS
Business Acquisition [Line Items]
Goodwill	33,017
Hoodoo Digital, LLC \| Customer-related intangible assets
Business Acquisition [Line Items]
Acquired intangibles	16,200
Hoodoo Digital, LLC \| Marketing-related intangible assets
Business Acquisition [Line Items]
Acquired intangibles	$ 2,400