Quarterly report pursuant to Section 13 or 15(d)

Concentrations of Credit Risk - Additional Information (Detail)

v3.8.0.1
Concentrations of Credit Risk - Additional Information (Detail)
$ in Thousands
3 Months Ended
Mar. 31, 2018
USD ($)
Customer
Mar. 31, 2017
Customer
Dec. 31, 2017
USD ($)
Concentration Risk [Line Items]      
Trade accounts receivable | $ $ 0   $ 0
Revenue Concentration [Member]      
Concentration Risk [Line Items]      
Concentration risk, number of customers | Customer 3 3  
Customer 1 [Member] | Revenue Concentration [Member] | Customer Concentration Risk [Member]      
Concentration Risk [Line Items]      
Concentration risk, percentage 80.00% 50.00%  
Customer 2 [Member] | Revenue Concentration [Member] | Customer Concentration Risk [Member]      
Concentration Risk [Line Items]      
Concentration risk, percentage 15.00% 30.00%  
Customer 3 [Member] | Revenue Concentration [Member] | Customer Concentration Risk [Member]      
Concentration Risk [Line Items]      
Concentration risk, percentage 5.00% 16.00%