Quarterly report pursuant to Section 13 or 15(d)

Concentrations of Credit Risk - Additional Information (Detail)

v3.10.0.1
Concentrations of Credit Risk - Additional Information (Detail)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2018
USD ($)
Customer
Jun. 30, 2017
Customer
Jun. 30, 2018
USD ($)
Customer
Jun. 30, 2017
Customer
Dec. 31, 2017
USD ($)
Concentration Risk [Line Items]          
Trade accounts receivable | $ $ 0   $ 0   $ 0
Revenue Concentration [Member]          
Concentration Risk [Line Items]          
Concentration risk, number of customers | Customer 1 2 1 2  
Revenue Concentration [Member] | Customer Concentration Risk [Member]          
Concentration Risk [Line Items]          
Concentration risk, percentage 99.00%   98.00%    
Customer 1 [Member] | Revenue Concentration [Member] | Customer Concentration Risk [Member]          
Concentration Risk [Line Items]          
Concentration risk, percentage   83.00%   72.00%  
Customer 2 [Member] | Revenue Concentration [Member] | Customer Concentration Risk [Member]          
Concentration Risk [Line Items]          
Concentration risk, percentage   12.00%   20.00%