Restructuring Charges - Changes to Restructuring Liability by Major Restructuring Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Restructuring Cost And Reserve [Line Items]
Beginning balance	$ 2,276	$ 1,944	$ 5,698
Restructuring charges (recoveries)	5,183	2,956	1,637
Cash payments	(3,866)	(2,572)	(5,276)
Adjustment to liability	189	(52)	(115)
Ending balance	3,782	2,276	1,944
GES Consolidation | Severance & Employee Benefits
Restructuring Cost And Reserve [Line Items]
Beginning balance	751	543	1,240
Restructuring charges (recoveries)	3,693	1,767	2,358
Cash payments	(2,170)	(1,514)	(3,055)
Adjustment to liability		(45)
Ending balance	2,274	751	543
GES Consolidation | Severance & Employee Benefits
Restructuring Cost And Reserve [Line Items]
Beginning balance	1,291	1,161	3,565
Restructuring charges (recoveries)	759	587	(828)
Cash payments	(1,150)	(457)	(1,376)
Adjustment to liability	192		(200)
Ending balance	1,092	1,291	1,161
Other Restructuring | Severance & Employee Benefits
Restructuring Cost And Reserve [Line Items]
Beginning balance	234	240	893
Restructuring charges (recoveries)	731	602	107
Cash payments	(546)	(601)	(845)
Adjustment to liability	(3)	(7)	85
Ending balance	$ 416	$ 234	$ 240