Segment Information (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues
Total revenues	$ 1,025,231	$ 942,364	$ 844,761
Exhibition and event services [Member]
Revenues
Total revenues	726,429	670,054	590,444
Exhibits and Environments [Member]
Revenues
Total revenues	175,611	170,496	166,040
Travel and Recreation Services [Member]
Revenues
Total revenues	$ 123,191	$ 101,814	$ 88,277