Accounts Receivable and Major Customers - Additional Information (Detail) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2015 USD ($) Customer	Jun. 30, 2014 USD ($) Customer	Dec. 31, 2014 USD ($)
Sales Revenue | Customer Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of major customers | Customer	3	4
Revenues, major customers	$ 96.7	$ 148.8
Concentration risk, percentage	62.00%	55.00%
Sales Revenue | Customer Concentration Risk | Major Customer 1
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	$ 41.2	$ 48.4
Concentration risk, percentage	26.00%	18.00%
Sales Revenue | Customer Concentration Risk | Major Customer 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	$ 36.1	$ 35.5
Concentration risk, percentage	23.00%	13.00%
Sales Revenue | Customer Concentration Risk | Major Customer 3
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	$ 19.4	$ 34.0
Concentration risk, percentage	13.00%	13.00%
Sales Revenue | Customer Concentration Risk | Major Customer 4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers		$ 30.9
Concentration risk, percentage		11.00%
Accounts Receivable | Credit Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk, percentage	50.00%		58.00%
Accounts receivable, major customers	$ 30.2		$ 36.1