Accounts Receivable and Major Customers - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012 Customer Concentration Risk Customer	Jun. 30, 2011 Customer Concentration Risk Customer	Jun. 30, 2012 Credit Concentration Risk	Dec. 31, 2011 Credit Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of major customers	6	6
Revenues, major customers	$ 79.5	$ 95.4
Percentage of revenue from major customers	50.00%	68.00%
Accounts receivable, major customers			$ 14.4	$ 29.8
Percentage of accounts receivable from major customers			26.00%	41.00%