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