Revenue and Related Contract Costs and Contract Liabilities - Balance Sheet Reclassifications made to Separately Present Contract Costs and Contract Liabilities in Connection with Adoption of Topic 606 (Details) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017		Jun. 30, 2017	Dec. 31, 2016
Disaggregation Of Revenue [Line Items]
Cash and cash equivalents		$ 49,386	$ 53,723		$ 44,042	$ 20,900
Accounts receivable, net		141,633	104,811
Inventories		20,361	17,550	[1]
Current contract costs		21,525	13,436	[1]
Other current assets		31,167	19,741	[1]
Property and equipment, net		324,951	305,571
Other investments and assets		49,580	48,187	[1]
Deferred income taxes		21,146	23,548
Goodwill		266,023	270,551
Other intangible assets, net		57,397	62,781
Total Assets		983,169	919,899
Accounts payable		96,569	77,380
Contract liabilities		50,419	31,981	[2]
Accrued compensation		29,280	30,614
Other current liabilities		47,711	40,154	[2]
Debt and capital lease obligations, current and long-term		239,478	209,192
Pension and postretirement benefits		27,661	28,135
Other deferred items and liabilities		49,357	52,858
Total liabilities		540,475	470,314
Redeemable noncontrolling interest		6,513	6,648
Total stockholders' equity		436,181	442,937	[3]	$ 413,721	$ 370,638
Total Liabilities and Stockholders’ Equity		$ 983,169	919,899
Accounting Standards Update 2014-09 | As Previously Reported
Disaggregation Of Revenue [Line Items]
Cash and cash equivalents			53,723
Accounts receivable, net			104,811
Inventories	[1]		30,372
Other current assets	[1]		21,030
Property and equipment, net			305,571
Other investments and assets	[1]		47,512
Deferred income taxes			23,548
Goodwill			270,551
Other intangible assets, net			62,781
Total Assets			919,899
Accounts payable			77,380
Customer deposits	[2]		33,415
Accrued compensation			30,614
Other current liabilities	[2]		38,720
Debt and capital lease obligations, current and long-term			209,192
Pension and postretirement benefits			28,135
Other deferred items and liabilities			52,858
Total liabilities			470,314
Redeemable noncontrolling interest			6,648
Total stockholders' equity	[3]		442,937
Total Liabilities and Stockholders’ Equity			919,899
Accounting Standards Update 2014-09 | Reclassifications
Disaggregation Of Revenue [Line Items]
Inventories	[1]		(12,822)
Current contract costs	[1]		13,436
Other current assets	[1]		(1,289)
Other investments and assets	[1]		675
Customer deposits	[2]		(33,415)
Contract liabilities	[2]		31,981
Other current liabilities	[2]		$ 1,434

[1] Contract costs primarily consist of deferred core services costs (including labor and vendor purchases) required to service future exhibitions, conferences and other events, and commission expenses incurred to obtain contracts. All such costs were previously included in “Inventories” and in certain other assets. As a result of the changes noted above, deferred core services costs related to exhibitions and events that are scheduled to occur longer than one year in the future are currently included in “Other investments and assets”. The impact of this change reduced total current assets at December 31, 2017 by $0.7 million. The amount of deferred core services costs included in “Other investments and assets” at June 30, 2018 was $5.1 million.

[2] 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.

[3] We determined that the cumulative effect of initially applying Topic 606 as an adjustment to the opening balance of retained earnings was not material, and therefore we made no adjustment.