Quarterly report pursuant to Section 13 or 15(d)

Accounts Receivable and Major Customers - Additional Information (Detail)

v3.8.0.1
Accounts Receivable and Major Customers - Additional Information (Detail)
$ in Millions
9 Months Ended 12 Months Ended
Sep. 30, 2017
USD ($)
Customer
Sep. 30, 2016
USD ($)
Customer
Dec. 31, 2016
USD ($)
Sales Revenue | Customer Concentration Risk      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Number of major customers | Customer 2 3  
Revenues, major customers $ 85.9 $ 93.5  
Concentration risk, percentage 82.00% 94.00%  
Sales Revenue | Customer Concentration Risk | Major Customer 1      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Revenues, major customers $ 72.6 $ 64.1  
Concentration risk, percentage 69.00% 64.00%  
Sales Revenue | Customer Concentration Risk | Major Customer 2      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Revenues, major customers $ 13.3 $ 15.8  
Concentration risk, percentage 13.00% 16.00%  
Sales Revenue | Customer Concentration Risk | Major Customer 3      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Revenues, major customers   $ 13.6  
Concentration risk, percentage   14.00%  
Accounts Receivable | Credit Concentration Risk      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Concentration risk, percentage 47.00%   81.00%
Accounts receivable, major customers $ 14.6   $ 16.7