Prepaid Expenses and Other Current Assets - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended			60 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012	Feb. 03, 2012
Hurricane
Prepaid Expenses And Other Current Assets [Line Items]
Estimated and paid insurance recoveries	$ 0.3
Decrease in revenue	0.3
Securities-Law Civil Actions And A Governmental Interaction
Prepaid Expenses And Other Current Assets [Line Items]
Class action settlement					7.0
Cumulative legal fees and costs				12.9
Insurance reimbursements	10.0			10.0
Legal fees	0.8	2.4	0.9
Estimated and paid insurance recoveries	$ 1.1	$ 2.4	$ 0.9