Segment Information (Reconciliation of Total Segment Operating Income to Consolidated Operating Income) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Revenues	$ 429,044	$ 330,984	$ 827,228	$ 663,377
Gross profit	365,707	274,182	706,068	547,444
Direct costs	271,423	201,142	533,304	419,157
Income from operations	94,284	73,040	172,764	128,287
Operating Segments
Segment Reporting Information [Line Items]
Revenues	429,044	330,984	827,228	663,376
Gross profit	365,716	274,219	706,142	547,480
Direct costs	258,576	189,522	504,885	395,391
Income from operations	107,140	84,697	201,257	152,089
Elimination of inter-segment
Segment Reporting Information [Line Items]
Revenues	(292)	(61)	(410)	(144)
Gross profit	(76)	(61)	(126)	(144)
Direct costs	(76)	(61)	(126)	(144)
Corporate
Segment Reporting Information [Line Items]
Revenues	0	0	0	1
Gross profit	(9)	(37)	(74)	(36)
Direct costs	12,847	11,620	28,419	23,766
Income from operations	(12,856)	(11,657)	(28,493)	(23,802)
Total Cloud Services \| Operating Segments
Segment Reporting Information [Line Items]
Revenues	175,359	167,058	346,788	336,842
Gross profit	137,094	127,631	271,509	259,055
Direct costs	74,060	62,835	145,001	135,320
Income from operations	63,034	64,796	126,508	123,735
Fax and Martech \| Operating Segments
Segment Reporting Information [Line Items]
Revenues	105,127	93,976	206,181	188,643
Gross profit	85,760	77,245	169,749	156,714
Direct costs	34,116	27,204	65,052	57,134
Income from operations	51,644	50,041	104,697	99,580
Voice, Backup, Security and CPP \| Operating Segments
Segment Reporting Information [Line Items]
Revenues	70,232	73,082	140,607	148,199
Gross profit	51,334	50,386	101,760	102,341
Direct costs	39,944	35,631	79,949	78,186
Income from operations	11,390	14,755	21,811	24,155
Digital Media \| Operating Segments
Segment Reporting Information [Line Items]
Revenues	253,977	163,987	480,850	326,678
Gross profit	228,698	146,649	434,759	288,569
Direct costs	184,592	126,748	360,010	260,215
Income from operations	$ 44,106	$ 19,901	$ 74,749	$ 28,354