Accounts Receivable - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2011 Customer Concentration Risk Entity	Sep. 30, 2010 Customer Concentration Risk Entity	Sep. 30, 2011 Credit Concentration Risk	Dec. 31, 2010 Credit Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of major customers	5	5
Revenues, major customers	$ 135.9	$ 123.0
Percentage of revenue from major customers	61.00%	66.00%
Accounts receivable, major customers			$ 24.8	$ 32.9
Percentage of accounts receivable from major customers			33.00%	45.00%