Accounts Receivable and Major Customers - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($) Customer	Sep. 30, 2015 USD ($) Customer	Dec. 31, 2015 USD ($)
Sales Revenue | Customer Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of major customers | Customer	3	2
Revenues, major customers	$ 93.5	$ 108.4
Concentration risk, percentage	94.00%	50.00%
Sales Revenue | Customer Concentration Risk | Major Customer 1
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	$ 64.1	$ 62.3
Concentration risk, percentage	64.00%	29.00%
Sales Revenue | Customer Concentration Risk | Major Customer 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	$ 15.8	$ 46.1
Concentration risk, percentage	16.00%	21.00%
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	88.00%	90.00%
Accounts receivable, major customers	$ 16.2		$ 21.1