Accounts Receivable and Major Customers - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015 Customer	Mar. 31, 2014 Customer	Dec. 31, 2014
Sales Revenue | Customer Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of major customers	3	4
Revenues, major customers	$ 47.9	$ 89.5
Concentration risk, percentage	66.00%	67.00%
Sales Revenue | Customer Concentration Risk | Major Customer 1
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	28.0	38.8
Concentration risk, percentage	38.00%	29.00%
Sales Revenue | Customer Concentration Risk | Major Customer 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	12.0	17.4
Concentration risk, percentage	17.00%	13.00%
Sales Revenue | Customer Concentration Risk | Major Customer 3
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	7.9	17.2
Concentration risk, percentage	11.00%	13.00%
Sales Revenue | Customer Concentration Risk | Major Customer 4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers		16.1
Concentration risk, percentage		12.00%
Accounts Receivable | Credit Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk, percentage	48.00%		58.00%
Accounts receivable, major customers	$ 27.4		$ 36.1