Segment Information - Total Assets, Capital Expenditures, Depreciation and Amortization (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting, Other Significant Reconciling Item [Line Items]
Assets	$ 3,770,280	$ 3,665,331
Assets of discontinued operations	0	567,551
Capital expenditures	113,740	92,552	$ 70,588
Depreciation and amortization	258,303	228,737	232,032
Reportable segments
Segment Reporting, Other Significant Reconciling Item [Line Items]
Assets	3,131,945	2,994,244
Capital expenditures	113,740	92,552	70,562
Depreciation and amortization	258,015	225,079	229,545
Corporate, Non-Segment
Segment Reporting, Other Significant Reconciling Item [Line Items]
Assets	638,335	103,536
Capital expenditures	0	0	26
Depreciation and amortization	288	3,658	2,487
Cybersecurity and Martech | Reportable segments
Segment Reporting, Other Significant Reconciling Item [Line Items]
Assets	1,088,741	905,847
Capital expenditures	32,863	32,859	21,826
Depreciation and amortization	64,354	79,758	80,970
Digital Media | Reportable segments
Segment Reporting, Other Significant Reconciling Item [Line Items]
Assets	2,043,204	2,088,397
Capital expenditures	80,877	59,693	48,736
Depreciation and amortization	$ 193,661	$ 145,321	$ 148,575