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Related Party Transactions - Additional Information (Detail) - USD ($)
1 Months Ended 3 Months Ended 9 Months Ended
Aug. 31, 2016
Sep. 30, 2017
Sep. 30, 2017
Dec. 31, 2016
Related Party Transaction [Line Items]        
Note receivable from affiliate   $ 36,700,000 $ 36,700,000 $ 27,400,000
Unsecured Revolving Demand Promissory | Valhi Inc        
Related Party Transaction [Line Items]        
Maximum loan amount $ 40,000,000      
Interest rate on loans repayment 1.00%      
Principal due on demand effective date Dec. 31, 2018      
Note receivable from affiliate   36,700,000 36,700,000  
Interest income including unused commitment fees on our loan   $ 500,000 $ 1,300,000