Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Line Items]
Operating loss carryforwards	$ 2.2
Operating loss carryforwards, expiration dates	2018
Statutory federal income tax rate	35.00%	35.00%	35.00%
Unrecognized tax benefits that would affect the tax provision and effective tax rate	22.6
Uncertain tax position, accrued interest	4.4	4.9
Minimum [Member]
Income Taxes [Line Items]
Additional tax payment in next year	3.0
Maximum [Member]
Income Taxes [Line Items]
Additional tax payment in next year	5.0
State [Member]
Income Taxes [Line Items]
Operating loss carryforwards	1,000.0
Operating loss carryforwards, expiration dates	2014 through 2031
Incremental state tax provision (expense)	0	8.5
Federal [Member]
Income Taxes [Line Items]
Operating loss carryforwards	8.5
Operating loss carryforwards, expiration dates	2029
Alternative minimum tax credit carryforward	$ 1.6