Accounts Receivable and Major Customers - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Customer	Dec. 31, 2013 Customer
Sales Revenue | Customer Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of major customers	3	3
Revenues, major customers	$ 258.7	$ 181.7
Concentration risk, percentage	50.00%	42.00%
Sales Revenue | Customer Concentration Risk | Major Customer 1
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	113.6	70.4
Concentration risk, percentage	22.00%	16.00%
Sales Revenue | Customer Concentration Risk | Major Customer 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	80.1	55.9
Concentration risk, percentage	16.00%	13.00%
Sales Revenue | Customer Concentration Risk | Major Customer 3
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	65.0	55.4
Concentration risk, percentage	12.00%	13.00%
Accounts Receivable | Credit Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk, percentage	58.00%	37.00%
Accounts receivable, major customers	$ 36.1	$ 34.8