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Goodwill and Intangible Assets (Changes in Carrying Amounts of Goodwill) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Feb. 09, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Goodwill [Line Items]
Balance as of January 1, 2021				$ 1,867,430
Goodwill acquired (Note 4)				53,013
Goodwill removed due to sale of a business				(1,339)
Goodwill reclassified to noncurrent assets held for sale				(48,632)
Goodwill impairment		$ (32,629)	$ 0	(32,629)	$ 0
Purchase accounting adjustments				2,650
Foreign exchange translation				(2,954)
Balance as of June 30, 2021		1,837,539		1,837,539
Voice, Backup, Security and CPP
Goodwill [Line Items]
Goodwill removed due to sale of a business	$ (1,300)
Operating Segments \| Total Cloud Services
Goodwill [Line Items]
Balance as of January 1, 2021				924,496
Goodwill acquired (Note 4)				39,519
Goodwill removed due to sale of a business				(1,339)
Goodwill reclassified to noncurrent assets held for sale				(48,632)
Goodwill impairment				(32,629)
Purchase accounting adjustments				47
Foreign exchange translation				(2,678)
Balance as of June 30, 2021		878,784		878,784
Operating Segments \| Fax and Martech
Goodwill [Line Items]
Balance as of January 1, 2021				425,471
Goodwill acquired (Note 4)				39,519
Goodwill removed due to sale of a business				0
Goodwill reclassified to noncurrent assets held for sale				0
Goodwill impairment				0
Purchase accounting adjustments				0
Foreign exchange translation				(1,861)
Balance as of June 30, 2021		463,129		463,129
Operating Segments \| Voice, Backup, Security and CPP
Goodwill [Line Items]
Balance as of January 1, 2021				499,025
Goodwill acquired (Note 4)				0
Goodwill removed due to sale of a business				(1,339)
Goodwill reclassified to noncurrent assets held for sale				(48,632)
Goodwill impairment				(32,629)
Purchase accounting adjustments				47
Foreign exchange translation				(817)
Balance as of June 30, 2021		415,655		415,655
Operating Segments \| Digital Media
Goodwill [Line Items]
Balance as of January 1, 2021				942,934
Goodwill acquired (Note 4)				13,494
Goodwill removed due to sale of a business				0
Goodwill reclassified to noncurrent assets held for sale				0
Goodwill impairment				0
Purchase accounting adjustments				2,603
Foreign exchange translation				(276)
Balance as of June 30, 2021		$ 958,755		$ 958,755