Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2012

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance

Open mark-to-market gains (losses) on derivatives included in operating revenues were as follows:

Years ended December 31, (in thousands)	2012		2011			2010
Mark-to-market gain (loss) on derivatives	$	58,750	$	(37,587	)	$	(3	)

Schedule of taxes other than income taxes

The collection and payment of revenue taxes such as utility license taxes and fees, franchise fees and taxes imposed by other governmental authorities are reported on a gross basis. These amounts are included in taxes other than income taxes on the consolidated statements of income as follows:

Years ended December 31, (in thousands)	2012		2011		2010
Taxes on revenues	$	21,479	$	25,268	$	30,704