Other Current Liabilities - Schedule of Other Current Liabilities (Parenthetical) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Other Liabilities Current [Line Items]
Reclassification of GES' events accommodation services deposits out of "Contract liabilities" to "Other current liabilities"	$ 40,132	$ 40,154	[1]
Reclassification of accrued rebates to contract liabilities	$ 58,260	31,981	[1]
Adopting Topic 606 | Reclassification of Contract Liabilities to Other Contract Liabilities
Other Liabilities Current [Line Items]
Reclassification of GES' events accommodation services deposits out of "Contract liabilities" to "Other current liabilities"		2,500
Adopting Topic 606 | Reclassification of Accrued Rebates to Contract Liabilities
Other Liabilities Current [Line Items]
Reclassification of accrued rebates to contract liabilities		$ 1,100

[1] In connection with the adoption of Topic 606, we elected to more prominently present contract liabilities on the Consolidated Balance Sheets. Consequently, customer deposits of $33.4 million as of December 31, 2017, have been reclassified to “Contract liabilities” and to other certain current liabilities to conform to the current period presentation.