Segment Information (Total Assets, Capital Expenditures, Depreciation and Amortization) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Segment Reporting, Other Significant Reconciling Item [Line Items]
Assets	$ 3,433,068		$ 3,433,068		$ 3,770,280
Capital expenditures			80,767	$ 87,495
Depreciation and amortization	55,937	$ 66,217	174,880	196,443
Reportable segments
Segment Reporting, Other Significant Reconciling Item [Line Items]
Assets	2,985,325		2,985,325		3,131,945
Capital expenditures			80,763	72,243
Depreciation and amortization	56,076	62,798	174,863	187,285
Corporate
Segment Reporting, Other Significant Reconciling Item [Line Items]
Assets	447,743		447,743		638,335
Capital expenditures			4	0
Depreciation and amortization	(139)	79	17	217
Discontinued operations
Segment Reporting, Other Significant Reconciling Item [Line Items]
Capital expenditures			0	15,252
Depreciation and amortization	0	3,340	0	8,941
Digital Media | Reportable segments
Segment Reporting, Other Significant Reconciling Item [Line Items]
Assets	2,014,843		2,014,843		2,043,204
Capital expenditures			69,451	51,995
Depreciation and amortization	44,631	50,056	138,297	147,482
Cybersecurity and Martech | Reportable segments
Segment Reporting, Other Significant Reconciling Item [Line Items]
Assets	970,482		970,482		$ 1,088,741
Capital expenditures			11,312	20,248
Depreciation and amortization	$ 11,445	$ 12,742	$ 36,566	$ 39,803