Goodwill and Intangible Assets (Changes in Carrying Amounts of Goodwill) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Goodwill [Roll Forward]
Beginning balance			$ 1,531,455
Goodwill acquired			93,827
Goodwill impairment	$ (27,369)	$ 0	(27,369)	$ (32,629)
Purchase accounting adjustments			4,806
Foreign exchange translation			(22,762)
Ending balance	1,579,957		1,579,957		$ 1,531,455
Digital Media
Goodwill [Roll Forward]
Goodwill impairment			(27,400)		0
Cybersecurity and Martech
Goodwill [Roll Forward]
Goodwill impairment			(32,600)		(32,600)
Operating Segments | Digital Media
Goodwill [Roll Forward]
Beginning balance			996,659
Goodwill acquired			93,827
Goodwill impairment	(27,400)		(27,369)
Purchase accounting adjustments			4,943
Foreign exchange translation			(5,952)
Ending balance	1,062,108		1,062,108		996,659
Operating Segments | Cybersecurity and Martech
Goodwill [Roll Forward]
Beginning balance			534,796
Goodwill acquired			0
Goodwill impairment			0
Purchase accounting adjustments			(137)
Foreign exchange translation			(16,810)
Ending balance	$ 517,849		$ 517,849		$ 534,796