Goodwill And Intangible Assets (Changes In Carrying Amounts Of Goodwill And Other Intangible Assets) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Goodwill [Line Items]
Balance as of January 1, 2020	$ 1,633,033
Goodwill acquired (Note 4)	16,741
Purchase accounting adjustments (1)	(2,553)
Foreign exchange translation	(10,028)
Balance as of March 31, 2020	1,637,193
Fax and Martech [Member]
Goodwill [Line Items]
Balance as of January 1, 2020	397,788
Goodwill acquired (Note 4)	16,119
Purchase accounting adjustments (1)	0
Foreign exchange translation	(1,325)
Balance as of March 31, 2020	412,582
Voice, Backup, Security and CPP [Member]
Goodwill [Line Items]
Balance as of January 1, 2020	480,084
Goodwill acquired (Note 4)	0
Purchase accounting adjustments (1)	(2,539)
Foreign exchange translation	(8,070)
Balance as of March 31, 2020	469,475
Cloud Services Segment [Member]
Goodwill [Line Items]
Balance as of January 1, 2020	877,872
Goodwill acquired (Note 4)	16,119
Purchase accounting adjustments (1)	(2,539)
Foreign exchange translation	(9,395)
Balance as of March 31, 2020	882,057
Digital Media Segment [Member]
Goodwill [Line Items]
Balance as of January 1, 2020	755,161
Goodwill acquired (Note 4)	622
Purchase accounting adjustments (1)	(14)
Foreign exchange translation	(633)
Balance as of March 31, 2020	$ 755,136