Segment Information (Reconciliation of Total Segment Operating Income to Consolidated Operating Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Revenues	$ 356,976	$ 344,141	$ 1,020,353	$ 966,466
Gross profit	301,154	282,425	848,598	793,471
Direct costs	223,716	223,066	642,873	626,636
Income from operations	77,438	59,359	205,725	166,835
Operating Segments
Segment Reporting Information [Line Items]
Revenues	356,976	344,138	1,020,352	966,460
Gross profit	301,165	282,422	848,645	793,465
Direct costs	209,326	215,984	617,321	605,628
Income from operations	91,839	66,438	231,324	187,837
Elimination of inter-segment
Segment Reporting Information [Line Items]
Revenues	(56)	(17)	(200)	(114)
Gross profit	(56)	(17)	(200)	(114)
Direct costs	(56)	(17)	(200)	(114)
Corporate
Segment Reporting Information [Line Items]
Revenues	0	3	1	6
Gross profit	(11)	3	(47)	6
Direct costs	14,390	7,082	25,552	21,008
Income from operations	(14,401)	(7,079)	(25,599)	(21,002)
Total Cloud Services | Operating Segments
Segment Reporting Information [Line Items]
Revenues	170,248	171,163	507,090	492,540
Gross profit	131,827	132,923	390,882	385,219
Direct costs	66,070	71,978	207,412	203,393
Income from operations	65,757	60,945	183,470	181,826
Fax and Martech | Operating Segments
Segment Reporting Information [Line Items]
Revenues	98,044	95,300	286,687	284,151
Gross profit	81,435	79,590	238,149	239,915
Direct costs	28,614	27,670	89,121	93,384
Income from operations	52,821	51,920	149,028	146,531
Voice, Backup, Security and CPP | Operating Segments
Segment Reporting Information [Line Items]
Revenues	72,204	75,863	220,403	208,389
Gross profit	50,392	53,333	152,733	145,304
Direct costs	37,456	44,308	118,291	110,009
Income from operations	12,936	9,025	34,442	35,295
Digital Media | Operating Segments
Segment Reporting Information [Line Items]
Revenues	186,784	172,992	513,462	474,034
Gross profit	169,394	149,516	457,963	408,360
Direct costs	143,312	144,023	410,109	402,349
Income from operations	$ 26,082	$ 5,493	$ 47,854	$ 6,011