Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Income Tax Disclosure [Abstract]
Income tax expense	$ 19,974	$ 50,205	$ 49,009	$ 98,830
Effective tax rates (percent)	33.60%	38.10%	30.30%	37.50%
Income tax expense credit from favorable outcome of state tax audits			$ 6,449