Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Additional Information (Detail)

v3.10.0.1
Summary of Significant Accounting Policies - Additional Information (Detail)
$ in Thousands
 3 Months Ended 9 Months Ended 12 Months Ended
Jul. 27, 2018
Sep. 30, 2018
USD ($)
Sep. 30, 2017
USD ($)
Sep. 30, 2018
USD ($)
Sep. 30, 2017
USD ($)
Dec. 31, 2017
USD ($)
Revenue, Major Customer [Line Items]            
Percentage accounted for under the equity method   50.00%   50.00%    
Revenues   $ 123,395 $ 118,308 $ 351,673 $ 326,186  
Deposits in domestic bank   41,300   41,300   $ 97,600
Uninsured deposits in foreign banks   42,400   $ 42,400   $ 45,600
Reverse stock split, conversion ratio 15          
Preferred dividend percentage       7.25%   7.25%
Reimbursable revenue            
Revenue, Major Customer [Line Items]            
Revenues   $ 13,400 $ 15,000 $ 40,400 45,500  
Exxon Neftegas Limited | Reimbursable revenue            
Revenue, Major Customer [Line Items]            
Revenues       $ 34,600 $ 39,900  
Customer Concentration Risk | Sales Revenue, Net | Exxon Neftegas Limited            
Revenue, Major Customer [Line Items]            
Percentage of revenue from major customer       25.70% 32.60%  
Customer Concentration Risk | Sales Revenue, Net Of Reimbursable Revenues | Exxon Neftegas Limited            
Revenue, Major Customer [Line Items]            
Percentage of revenue from major customer       17.90% 23.60%  
Minimum            
Revenue, Major Customer [Line Items]            
Estimated Useful Life (Years)       3 years    
Maximum            
Revenue, Major Customer [Line Items]            
Estimated Useful Life (Years)       6 years