Overview and Basis of Presentation - Schedule of Corrections to Prior Period Adjustments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Total revenue	$ 63,072	$ 353,743	$ 389,863	$ 1,009,686
Services
Total revenue	43,702	291,701	335,383	858,071
Costs and expenses	51,730	247,551	395,432	785,131
GES
Total revenue	$ 14,257	218,700	$ 322,261	808,567
Previously Reported | Services
Total revenue		300,446		898,746
Costs and expenses		256,296		825,806
Revision Of Prior Period Error Correction Adjustment | GES | Services | North America
Total revenue		(6,859)		(32,081)
Costs and expenses		(6,859)		(32,081)
Revision Of Prior Period Error Correction Adjustment | GES | Services | EMEA
Total revenue		(1,886)		(8,594)
Costs and expenses		$ (1,886)		$ (8,594)