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Related Party Transactions - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Related Party Transaction [Line Items]      
Purchase of non-controlling interests $ 65,000 $ 308,000  
Partnership And Trust [Member]      
Related Party Transaction [Line Items]      
Purchase of non-controlling interests $ 65,000 $ 308,000 $ 308,000
Related Party [Member]      
Related Party Transaction [Line Items]      
Purchase of treasury stock shares 10,000 10,000