Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012	Dec. 31, 2011
Deferred Tax Liability Not Recognized [Line Items]
Total unrecognized tax benefits	$ 1.7	$ 1.7	$ 1.7
Accrued interest (net of tax benefit) related to uncertain tax positions	0	0	0
Net operating loss carryforward, expiration year		2031
Deferred tax assets, valuation allowance adjustment	(5.4)
Deferred tax assets, valuation allowance	90.1	90.1	95.5
Deferred tax assets, provision for valuation allowance	3.7	3.7	3.8
Deferred tax assets, decrease in valuation allowance		0.1
Internal Revenue Service (IRS)
Deferred Tax Liability Not Recognized [Line Items]
Net operating loss carryforward	80.8	80.8	92.0
State and Local Jurisdiction
Deferred Tax Liability Not Recognized [Line Items]
Net operating loss carryforward	$ 601.4	$ 601.4	$ 612.6