Segment Information (Reconciliation of Total Segment Operating Income to Consolidated Operating Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
Revenues	$ 315,068	$ 311,657
Gross profit	268,968	267,805
Direct costs	238,415	240,924
Income from operations	30,562	26,881
Reportable segments
Segment Reporting Information [Line Items]
Revenues	315,068	311,657
Gross profit	268,968	267,870
Direct costs	224,520	225,352
Income from operations	44,448	42,518
Elimination of inter-segment revenues
Segment Reporting Information [Line Items]
Revenues	(253)	(118)
Gross profit	(131)	(118)
Direct costs	(131)	(118)
Corporate
Segment Reporting Information [Line Items]
Revenues	0	0
Gross profit	0	(65)
Direct costs	13,895	15,572
Income from operations	(13,886)	(15,637)
Digital Media | Reportable segments
Segment Reporting Information [Line Items]
Revenues	234,827	226,874
Gross profit	209,706	206,081
Direct costs	177,586	175,428
Income from operations	32,120	30,653
Cybersecurity and Martech | Reportable segments
Segment Reporting Information [Line Items]
Revenues	80,494	84,901
Gross profit	59,393	61,907
Direct costs	47,065	50,042
Income from operations	$ 12,328	$ 11,865