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Investment in Affiliate - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Investments In And Advances To Affiliates [Line Items]      
Duration of prison management contract with an agency of the United Kingdom government 25 years    
Working capital loan to APM $ 3,100,000    
Equity earnings (losses) of joint venture (62,000) $ (41,000) $ (126,000)
Other assets      
Investments In And Advances To Affiliates [Line Items]      
Equity in net earnings of Affiliate $ 200,000    
Agecroft Prison Management Ltd      
Investments In And Advances To Affiliates [Line Items]      
Variable interest entity, ownership percentage 50.00%