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Summary of Significant Accounting Policies - Cash and Cash Equivalents (Detail) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Mar. 31, 2017
Dec. 31, 2016
Cash and Cash Equivalents [Line Items]        
Cash and cash equivalents $ 101,736 $ 138,285 $ 106,514 $ 112,183
Cash equivalents 7,100 7,100    
Domestic Bank Accounts        
Cash and Cash Equivalents [Line Items]        
Cash and cash equivalents 78,000 83,100    
Foreign Bank Accounts        
Cash and Cash Equivalents [Line Items]        
Cash and cash equivalents 23,700 55,200    
Investments in Joint Ventures        
Cash and Cash Equivalents [Line Items]        
Cash and cash equivalents 11,300 16,700    
Domestic Joint Ventures        
Cash and Cash Equivalents [Line Items]        
Cash and cash equivalents $ 10,600 $ 10,000