Accounts Receivable and Major Customers - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Customer	Dec. 31, 2011 Customer
Sales Revenue | Customer Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of major customers	4	3
Revenues, major customers	$ 182.0	$ 120.4
Concentration risk, percentage	59.00%	40.00%
Sales Revenue | Customer Concentration Risk | Major Customer 1
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	60.1	51.7
Concentration risk, percentage	19.00%	17.00%
Sales Revenue | Customer Concentration Risk | Major Customer 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	46.7	34.6
Concentration risk, percentage	15.00%	12.00%
Sales Revenue | Customer Concentration Risk | Major Customer 3
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	41.5	34.1
Concentration risk, percentage	14.00%	11.00%
Sales Revenue | Customer Concentration Risk | Major Customer 4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	33.8
Concentration risk, percentage	11.00%
Accounts Receivable | Credit Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk, percentage	34.00%	24.00%
Accounts receivable, major customers	$ 21.6	$ 17.2