Annual report pursuant to Section 13 and 15(d)

Accounts Receivable and Major Customers - Additional Information (Detail)

v3.6.0.2
Accounts Receivable and Major Customers - Additional Information (Detail)
$ in Millions
12 Months Ended
Dec. 31, 2016
USD ($)
Customer
Dec. 31, 2015
USD ($)
Customer
Sales Revenue | Customer Concentration Risk    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Number of major customers | Customer 3 3
Revenues, major customers $ 122.7 $ 168.9
Concentration risk, percentage 93.00% 64.00%
Sales Revenue | Customer Concentration Risk | Major Customer 1    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Revenues, major customers $ 93.5 $ 74.5
Concentration risk, percentage 71.00% 28.00%
Sales Revenue | Customer Concentration Risk | Major Customer 2    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Revenues, major customers $ 15.7 $ 63.5
Concentration risk, percentage 12.00% 24.00%
Sales Revenue | Customer Concentration Risk | Major Customer 3    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Revenues, major customers $ 13.5 $ 30.9
Concentration risk, percentage 10.00% 12.00%
Accounts Receivable | Credit Concentration Risk    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Concentration risk, percentage 81.00% 90.00%
Accounts receivable, major customers $ 16.7 $ 21.1