Operating Segments and Geographic Information - Reconciliation of Total Reportable Segments' Revenues and EBITDA to Consolidated Revenues and Consolidated Income Before Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Segment Revenues	$ 1,862,716	$ 2,131,278	$ 2,165,702
Amortization of intangibles	(64,395)	(74,609)	(75,140)
Depreciation expense	(42,500)	(40,400)	(38,300)
Severance, restructuring, and acquisition integration costs	(12,258)	(26,544)	(22,625)
Gain from patent litigation	0	0	62,141
Operating income	125,410	207,207	314,008
Interest expense, net	(58,888)	(55,814)	(60,839)
Non-operating pension benefit (cost)	(395)	1,017	(99)
Loss on debt extinguishment	0	0	(22,990)
Consolidated income from continuing operations before taxes	66,127	152,410	230,080
Reportable Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Segment Revenues	1,862,716	2,131,278	2,165,702
Deferred revenue adjustments	0	0	0
Total Segment EBITDA	246,959	353,035	394,660
Amortization of intangibles	(64,395)	(74,609)	(75,140)
Depreciation expense	(42,470)	(40,409)	(38,309)
Severance, restructuring, and acquisition integration costs	(12,258)	(26,544)	(22,625)
Purchase accounting effects related to acquisitions	(125)	(592)	(1,690)
Amortization of software development intangible assets	(1,821)	(525)	(79)
Loss on sale of assets	0	0	(94)
Costs related to patent litigation	0	0	(2,634)
Gain from patent litigation	0	0	62,141
Operating income	125,410	207,207	314,008
Interest expense, net	(58,888)	(55,814)	(60,839)
Eliminations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Operating income	(480)	(3,149)	(2,222)
Segment revenues | Reportable Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Segment Revenues	$ 1,862,716	$ 2,131,278	$ 2,165,702