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Revenue and Related Contract Costs and Contract Liabilities - Narrative (Details) - USD ($)
 3 Months Ended 12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disaggregation Of Revenue [Line Items]                      
Capitalized contract costs to obtain contracts $ 2,500,000               $ 2,500,000    
Capitalized contract costs to fulfill contracts 19,000,000               19,000,000    
Impairment loss on capitalized contract costs                 0    
Increase to net income on adopting Topic 606 $ (2,322,000) $ 37,389,000 $ 23,490,000 $ (9,387,000) $ (21,674,000) $ 44,657,000 $ 27,947,000 $ 6,777,000 49,170,000 $ 57,707,000 $ 42,269,000
Accounting Standards Update 2014-09 | Effect of Change                      
Disaggregation Of Revenue [Line Items]                      
Additional capitalized contracts costs                 1,700,000    
Increase to net income on adopting Topic 606                 $ 1,300,000    
GES                      
Disaggregation Of Revenue [Line Items]                      
Performance obligation description of payment terms                 Payment terms are generally within 30-60 days and contain no significant financing components    
GES | Minimum                      
Disaggregation Of Revenue [Line Items]                      
Performance obligation payment terms                 30 days    
GES | Maximum                      
Disaggregation Of Revenue [Line Items]                      
Performance obligation payment terms                 60 days    
Pursuit                      
Disaggregation Of Revenue [Line Items]                      
Performance obligation description of payment terms                 When credit is extended, payment terms are generally within 30 days and contain no significant financing components    
Performance obligation payment terms                 30 days