Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets
Allowance for doubtful accounts	$ 9,979	$ 9,098
Deferred and other compensation	10,636	18,165
Capital investments	3,790	3,780
Debt, capitalized fees, and other interest	2,291	4,644
Pension and other post-employment benefits	51,231	52,219
Operating lease liability	7,539	9,736
Reserve for facility exit costs	7,053	1,875
Net operating loss and credit carryforwards	28,611	27,019
Fixed assets and capitalized software	420	130
Non-compete and other agreements	46,213	30,250
Goodwill and other intangible assets	8,335	0
Other, net	8,566	11,239
Total deferred tax assets	184,664	168,155
Valuation allowance	(24,307)	(126,321)	$ (127,294)	$ (136,766)
Net deferred tax assets	160,357	41,834
Deferred tax liabilities
Goodwill and other intangibles	0	(1,658)
Deferred revenue	(46,501)	(71,943)
Deferred costs	(3,003)	(3,453)
Investment in subsidiaries	(5,466)	(4,676)
Operating lease right-of-use assets	(9,362)	(10,643)
Other, net	(3,434)	(4,199)
Total deferred tax liabilities	(67,766)	(96,572)
Net deferred tax asset (liability)	$ 92,591
Net deferred tax asset (liability)		$ (54,738)