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 9 Months Ended
Sep. 30, 2018
USD ($)
Customer
Sep. 30, 2017
Customer
Sep. 30, 2018
USD ($)
Customer
Sep. 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 2 4 3 4  
Customer 1 [Member] | Revenue Concentration [Member] | Customer Concentration Risk [Member]          
Concentration Risk [Line Items]          
Concentration risk, percentage 94.00% 63.00% 86.00% 64.20%  
Customer 2 [Member] | Revenue Concentration [Member] | Customer Concentration Risk [Member]          
Concentration Risk [Line Items]          
Concentration risk, percentage 6.00% 19.50% 11.00% 25.80%  
Customer 3 [Member] | Revenue Concentration [Member] | Customer Concentration Risk [Member]          
Concentration Risk [Line Items]          
Concentration risk, percentage   12.60% 2.00% 8.00%  
Customer 4 [Member] | Revenue Concentration [Member] | Customer Concentration Risk [Member]          
Concentration Risk [Line Items]          
Concentration risk, percentage   4.80%   2.00%