Accounts Receivable and Major Customers - Additional Information (Detail) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($) Customer	Sep. 30, 2014 USD ($) Customer	Dec. 31, 2014 USD ($)
Sales Revenue | Customer Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of major customers | Customer	2	4
Revenues, major customers	$ 108.4	$ 267.0
Concentration risk, percentage	50.00%	65.00%
Sales Revenue | Customer Concentration Risk | Major Customer 1
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	$ 62.3	$ 86.2
Concentration risk, percentage	29.00%	21.00%
Sales Revenue | Customer Concentration Risk | Major Customer 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	$ 46.1	$ 72.5
Concentration risk, percentage	21.00%	18.00%
Sales Revenue | Customer Concentration Risk | Major Customer 3
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers		$ 55.7
Concentration risk, percentage		13.00%
Sales Revenue | Customer Concentration Risk | Major Customer 4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers		$ 52.6
Concentration risk, percentage		13.00%
Accounts Receivable | Credit Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk, percentage	45.00%		63.00%
Accounts receivable, major customers	$ 16.5		$ 39.3