Segment Information Reportable Segment Information (Reconciliation of Total Segment Operating Income to Consolidated Operating Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Total revenues	$ 330,984	$ 322,432	$ 663,377	$ 622,325
Gross Profit	274,182	262,166	547,444	511,046
Direct Costs By Segment	201,142	205,552	419,157	403,570
Income from operations	73,040	56,614	128,287	107,476
Fax and Martech [Member]
Segment Reporting Information [Line Items]
Total revenues	93,976	95,567	188,643	188,850
Gross Profit	77,245	81,141	156,714	160,326
Direct Costs By Segment	28,789	31,455	60,507	65,689
Income from operations	48,456	49,686	96,207	94,637
Voice, Backup, Security and CPP [Member]
Segment Reporting Information [Line Items]
Total revenues	73,082	73,565	148,199	132,527
Gross Profit	50,386	51,393	102,341	91,970
Direct Costs By Segment	36,863	38,732	80,835	65,726
Income from operations	13,523	12,661	21,506	26,244
Cloud Services Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	167,058	169,132	336,842	321,377
Gross Profit	127,631	132,534	259,055	252,296
Direct Costs By Segment	65,652	70,187	141,342	131,415
Income from operations	61,979	62,347	117,713	120,881
Digital Media Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	163,987	153,359	326,678	301,042
Gross Profit	146,649	129,691	288,569	258,844
Direct Costs By Segment	129,829	128,158	266,797	258,326
Income from operations	16,820	1,533	21,772	518
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Total revenues	(61)	(61)	(144)	(97)
Gross Profit	(61)	(61)	(144)	(97)
Direct Costs By Segment	(61)	(61)	(144)	(97)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	330,984	322,430	663,376	622,322
Gross Profit	274,219	262,164	547,480	511,043
Direct Costs By Segment	195,420	198,284	407,995	389,644
Income from operations	78,799	63,880	139,485	121,399
Corporate [Member]
Segment Reporting Information [Line Items]
Total revenues	0	2	1	3
Gross Profit	(37)	2	(36)	3
Direct Costs By Segment	5,722	7,268	11,162	13,926
Global Operating Costs	$ (5,759)	$ (7,266)	$ 11,198	$ 13,923