Overview and Basis of Presentation - Impact of Adopting Topic 606 on Condensed Consolidated Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue:
GES services	$ 237,793
GES products	29,913
Pursuit services	7,755
Pursuit products	1,967
Costs and expenses:
Costs of services	257,295	$ 280,638
Costs of products	31,122	32,102
Income tax expense (benefit)	(4,638)	2,741
Net loss	(9,835)	$ 6,513
Calculated under Revenue Guidance in Effect before Topic 606 | Accounting Standards Update 2014-09
Revenue:
GES services	237,793
GES products	29,913
Pursuit services	7,755
Pursuit products	1,967
Costs and expenses:
Costs of services	258,142
Costs of products	31,122
Income tax expense (benefit)	(4,852)
Net loss	(10,468)
Effect of Change | Accounting Standards Update 2014-09
Costs and expenses:
Costs of services	(847)
Income tax expense (benefit)	214
Net loss	$ (633)