Taxes Other Than Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Taxes Other Than Income [Domain]
Taxes, Other	$ 344,460	$ 328,458	$ 289,941
Real Estate Taxes [Member]
Taxes, Other	58,117	57,889	47,934
Production Taxes [Member]
Taxes, Other	220,857	202,536	183,307
Payroll Taxes [Member]
Taxes, Other	59,186	54,631	48,702
Capital Stock and Franchise Tax [Member]
Taxes, Other	3,670	11,201	8,895
Virginia employment enhancement tax credit [Member]
Taxes, Other	(6,109)	(4,777)	(3,715)
Other taxes [Member]
Taxes, Other	$ 8,739	$ 6,978	$ 4,818