Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2011	Mar. 31, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Income Taxes [Abstract]
Effective tax rate (in hundredths)	20.20%		29.20%	21.80%	30.10%
Favorably impacted by net discrete items	$ 22,338			$ 30,354
Amount of net discrete items favorably impacting the effective tax rate arising principally from settlements with state taxing authorities		$ 8,016
Effective tax rate excluding discrete items (in hundredths)	27.40%			27.30%