Restructuring Charges - Changes to Restructuring Liability by Major Restructuring Activity (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Restructuring Cost And Reserve [Line Items]
Beginning balance				$ 5,230
Restructuring charges		$ 2,186	$ 11,259	5,799	$ 12,370
Cash payments				(4,379)
Non-cash items	[1]			(1,890)
Adjustment to liability				(44)
Ending balance		4,716		4,716
GES | Severance & Employee Benefits
Restructuring Cost And Reserve [Line Items]
Beginning balance				2,440
Restructuring charges				1,640
Cash payments				(992)
Adjustment to liability				(5)
Ending balance		3,083		3,083
GES | Facilities
Restructuring Cost And Reserve [Line Items]
Beginning balance				2,766
Restructuring charges				4,059
Cash payments				(3,296)
Non-cash items	[1]			(1,890)
Adjustment to liability				(26)
Ending balance		1,613		1,613
Other Restructuring | Severance & Employee Benefits
Restructuring Cost And Reserve [Line Items]
Beginning balance				24
Restructuring charges				100
Cash payments				(91)
Adjustment to liability				(13)
Ending balance		$ 20		$ 20

[1] Represents non-cash adjustments related to a write down of certain ROU assets as a result of vacating certain facilities prior to the lease term and the closure and liquidation of GES’ United Kingdom-based audio-visual services business.