Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies (Detail)

v3.19.3
Summary of Significant Accounting Policies (Detail)
$ in Thousands
3 Months Ended 6 Months Ended 9 Months Ended
Sep. 30, 2019
USD ($)
country
Mar. 31, 2019
USD ($)
Sep. 30, 2018
USD ($)
Sep. 30, 2019
USD ($)
country
Sep. 30, 2019
USD ($)
country
Sep. 30, 2018
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Revenue, Major Customer [Line Items]                
Number of countries in which entity has operated since inception | country 60     60 60      
Percentage accounted for under the equity method 50.00%     50.00% 50.00%      
Cash and cash equivalents $ 101,106     $ 101,106 $ 101,106   $ 48,602  
Restricted cash 0     0 0   10,389  
Cash, cash equivalents and restricted cash at end of period 101,106 $ 149,285 $ 81,728 101,106 101,106 $ 81,728 58,991 $ 141,549
Revenues 160,083 157,397 123,395 316,114   351,673    
Deposits in domestic banks in excess of federally insured limits 62,307     62,307 62,307   27,520  
Uninsured deposits in foreign banks 39,495     39,495 $ 39,495   32,907  
Reimbursable revenue                
Revenue, Major Customer [Line Items]                
Revenues $ 23,152 28,541 $ 13,404 41,617   40,440    
Exxon Neftegas Limited | Reimbursable revenue                
Revenue, Major Customer [Line Items]                
Revenues   $ 26,300   $ 37,100   $ 34,600    
Customer Concentration Risk | Sales Revenue, Net | Exxon Neftegas Limited                
Revenue, Major Customer [Line Items]                
Percentage of revenue from major customer   31.20%   27.70%   25.70%    
Customer Concentration Risk | Sales Revenue, Net | Exxon Neftegas Limited | Reimbursable revenue                
Revenue, Major Customer [Line Items]                
Percentage of revenue from major customer   17.70%   18.40%        
Minimum                
Revenue, Major Customer [Line Items]                
Estimated Useful Life (Years)         3 years      
Maximum                
Revenue, Major Customer [Line Items]                
Estimated Useful Life (Years)         6 years      
Compensating Balances                
Revenue, Major Customer [Line Items]                
Restricted cash             600  
Collateral on Letters of Credit                
Revenue, Major Customer [Line Items]                
Restricted cash             $ 9,800