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 9 Months Ended
Dec. 31, 2016
USD ($)
Customer
Sep. 30, 2017
USD ($)
Customer
Sep. 30, 2016
Customer
Sep. 30, 2017
USD ($)
Customer
Sep. 30, 2016
Customer
Concentration Risk [Line Items]          
Trade accounts receivable | $ $ 110 $ 0   $ 0  
Trade Accounts Receivable [Member]          
Concentration Risk [Line Items]          
Concentration risk, number of customers 1        
Revenue Concentration [Member]          
Concentration Risk [Line Items]          
Concentration risk, number of customers   3 4 3 4
Customer 1 [Member] | Trade Accounts Receivable [Member] | Customer Concentration Risk [Member]          
Concentration Risk [Line Items]          
Concentration risk, percentage 100.00%        
Customer 1 [Member] | Revenue Concentration [Member] | Customer Concentration Risk [Member]          
Concentration Risk [Line Items]          
Concentration risk, percentage   12.60% 16.20% 64.20% 15.00%
Customer 2 [Member] | Revenue Concentration [Member] | Customer Concentration Risk [Member]          
Concentration Risk [Line Items]          
Concentration risk, percentage   19.50% 18.60% 8.00% 22.90%
Customer 3 [Member] | Revenue Concentration [Member] | Customer Concentration Risk [Member]          
Concentration Risk [Line Items]          
Concentration risk, percentage   63.00% 27.50% 25.80% 25.40%
Customer 4 [Member] | Revenue Concentration [Member] | Customer Concentration Risk [Member]          
Concentration Risk [Line Items]          
Concentration risk, percentage     35.50%   32.80%