Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Additional Information (Detail)

v3.19.1
Summary of Significant Accounting Policies - Additional Information (Detail)
$ in Thousands
 3 Months Ended
Mar. 31, 2019
USD ($)
Mar. 31, 2018
USD ($)
Dec. 31, 2018
USD ($)
country
Dec. 31, 2017
USD ($)
Revenue, Major Customer [Line Items]        
Number of countries in which entity has operated since inception | country     60  
Percentage accounted for under the equity method 50.00%      
Cash and cash equivalents $ 127,849   $ 48,602  
Restricted cash 21,436   10,389  
Cash, cash equivalents and restricted cash at end of period 149,285 $ 118,315 58,991 $ 141,549
Revenues 157,397 109,675    
Deposits in domestic bank 118,300   27,500  
Uninsured deposits in foreign banks 35,300   32,900  
Reimbursable revenue        
Revenue, Major Customer [Line Items]        
Revenues 28,500 14,300    
Exxon Neftegas Limited | Reimbursable revenue        
Revenue, Major Customer [Line Items]        
Revenues $ 26,300 $ 12,100    
Customer Concentration Risk | Sales Revenue, Net | Exxon Neftegas Limited        
Revenue, Major Customer [Line Items]        
Percentage of revenue from major customer 31.20% 28.60%    
Customer Concentration Risk | Sales Revenue, Net Of Reimbursable Revenues | Exxon Neftegas Limited        
Revenue, Major Customer [Line Items]        
Percentage of revenue from major customer 17.70% 20.10%    
Minimum        
Revenue, Major Customer [Line Items]        
Estimated Useful Life (Years) 3 years      
Maximum        
Revenue, Major Customer [Line Items]        
Estimated Useful Life (Years) 6 years      
Professional Fees Escrow Account        
Revenue, Major Customer [Line Items]        
Restricted cash $ 20,600      
Compensating Balances        
Revenue, Major Customer [Line Items]        
Restricted cash $ 800   600  
Collateral on Letters of Credit        
Revenue, Major Customer [Line Items]        
Restricted cash     $ 9,800