Accounts Receivable - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 Entity	Dec. 31, 2010 Entity
Customer Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of major customers	5	5
Revenues, major customers	$ 173.1	$ 140.2
Percentage of revenue from major customers	58.00%	56.00%
Credit Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, major customers	$ 31.6	$ 31.1
Percentage of accounts receivable from major customers	44.00%	43.00%