Segment Information (Reconciliation of Total Segment Operating Income to Consolidated Operating Income) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Revenues	$ 444,252	$ 356,976	$ 1,271,480	$ 1,020,353
Gross profit	379,950	301,154	1,086,018	848,598
Direct costs	283,809	223,716	849,742	642,873
Income from operations	96,141	77,438	236,276	205,725
Operating Segments
Segment Reporting Information [Line Items]
Revenues	444,252	356,976	1,271,480	1,020,352
Gross profit	379,950	301,165	1,086,092	848,645
Direct costs	268,443	209,326	805,957	617,321
Income from operations	111,507	91,839	280,135	231,324
Elimination of inter-segment
Segment Reporting Information [Line Items]
Revenues	(356)	(56)	(766)	(200)
Gross profit	(88)	(56)	(214)	(200)
Direct costs	(88)	(56)	(214)	(200)
Corporate
Segment Reporting Information [Line Items]
Revenues	0	0	0	1
Gross profit	0	(11)	(74)	(47)
Direct costs	15,366	14,390	43,785	25,552
Income from operations	(15,366)	(14,401)	(43,859)	(25,599)
Digital Media \| Operating Segments
Segment Reporting Information [Line Items]
Revenues	262,429	186,784	743,280	513,462
Gross profit	238,650	169,394	673,409	457,963
Direct costs	188,950	143,312	548,960	410,109
Income from operations	49,700	26,082	124,449	47,854
Total Cloud Services \| Operating Segments
Segment Reporting Information [Line Items]
Revenues	182,179	170,248	528,966	507,090
Gross profit	141,388	131,827	412,897	390,882
Direct costs	79,581	66,070	257,211	207,412
Income from operations	61,807	65,757	155,686	183,470
Fax and Martech \| Operating Segments
Segment Reporting Information [Line Items]
Revenues	114,648	98,044	320,829	286,687
Gross profit	91,993	81,435	261,742	238,149
Direct costs	42,057	28,614	107,109	89,121
Income from operations	49,936	52,821	154,633	149,028
Voice, Backup, Security and CPP \| Operating Segments
Segment Reporting Information [Line Items]
Revenues	67,531	72,204	208,137	220,403
Gross profit	49,395	50,392	151,155	152,733
Direct costs	37,524	37,456	150,102	118,291
Income from operations	$ 11,871	$ 12,936	$ 1,053	$ 34,442