Goodwill And Intangible Assets (Changes In Carrying Amounts Of Goodwill And Other Intangible Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Beginning balance	$ 1,196,611	$ 1,122,810
Goodwill acquired (Note 4)	194,282	121,827	$ 333,190
Goodwill, Written off Related to Sale of Business Unit (1)(2)(3)		(57,741)
Purchase Accounting Adjustments (4)	774	(5,433)
Foreign exchange translation	(9,743)	(15,148)
Ending balance	1,380,376	1,196,611	1,122,810
Goodwill, Other Increase (Decrease)	0
Fax and Email Marketing [Member]
Goodwill [Roll Forward]
Beginning balance	346,814	319,734
Goodwill acquired (Note 4)	5,561	22,724
Goodwill, Written off Related to Sale of Business Unit (1)(2)(3)		0
Purchase Accounting Adjustments (4)	0	(741)
Foreign exchange translation	2,146	(5,097)
Ending balance	366,270	346,814	319,734
Goodwill, Other Increase (Decrease)	16,041
Voice, Backup, and Security [Member]
Goodwill [Roll Forward]
Beginning balance	256,939	239,418
Goodwill acquired (Note 4)	67,817	11,311
Goodwill, Written off Related to Sale of Business Unit (1)(2)(3)		(3,614)
Purchase Accounting Adjustments (4)	(1,014)	(25)
Foreign exchange translation	6,983	(9,849)
Ending balance	300,718	256,939	239,418
Goodwill, Other Increase (Decrease)	(16,041)
Cloud Services
Goodwill [Roll Forward]
Beginning balance	603,753	559,152
Goodwill acquired (Note 4)	73,378	34,035
Goodwill, Written off Related to Sale of Business Unit (1)(2)(3)		(3,614)
Purchase Accounting Adjustments (4)	(1,014)	(766)	800
Foreign exchange translation	(9,129)	(14,946)
Ending balance	666,988	603,753	559,152
Goodwill, Other Increase (Decrease)	0
Digital Media
Goodwill [Roll Forward]
Beginning balance	592,858	563,658
Goodwill acquired (Note 4)	120,904	87,792
Goodwill, Written off Related to Sale of Business Unit (1)(2)(3)		(54,127)
Purchase Accounting Adjustments (4)	(240)	(4,667)	5,000
Foreign exchange translation	(614)	(202)
Ending balance	713,388	$ 592,858	$ 563,658
Goodwill, Other Increase (Decrease)	0
Cambridge [Member] \| Digital Media
Goodwill [Roll Forward]
Goodwill, Written off Related to Sale of Business Unit (1)(2)(3)	(17,800)
Web24 [Member] \| Cloud Services [Member]
Goodwill [Roll Forward]
Goodwill, Written off Related to Sale of Business Unit (1)(2)(3)	(3,600)
Tea Leaves [Member] \| Digital Media
Goodwill [Roll Forward]
Goodwill, Written off Related to Sale of Business Unit (1)(2)(3)	$ (36,300)

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of divestiture of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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