Restructuring Charges - Changes to Restructuring Liability by Major Restructuring Activity (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Restructuring Cost And Reserve [Line Items]
Beginning balance				$ 4,513
Restructuring charges		$ 11,259	$ 1,702	12,370	$ 6,845
Cash payments				(4,027)
Non-cash items	[1]			(5,152)
Adjustment to liability				(683)
Ending balance		7,021		7,021
GES | Severance & Employee Benefits
Restructuring Cost And Reserve [Line Items]
Beginning balance				2,935
Restructuring charges				5,332
Cash payments				(3,261)
Adjustment to liability				(54)
Ending balance		4,952		4,952
GES | Facilities
Restructuring Cost And Reserve [Line Items]
Beginning balance				1,339
Restructuring charges				6,039
Cash payments				(197)
Non-cash items	[1]			(5,152)
Adjustment to liability				(17)
Ending balance		2,012		2,012
Other Restructuring | Severance & Employee Benefits
Restructuring Cost And Reserve [Line Items]
Beginning balance				239
Restructuring charges				999
Cash payments				(569)
Adjustment to liability				(612)
Ending balance		$ 57		$ 57

[1] (1) Represents the FX impact related to the closure and liquidation of GES’ United Kingdom-based audio-visual services business during the three months ended September 30, 2020.