Summarized Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2011

Summarized Quarterly Financial Data (Unaudited) [Abstract]

Summarized Quarterly Financial Data (Unaudited)

17.  Summarized Quarterly Financial Data (Unaudited)

	Quarter Ended
(Amounts in thousands, except per share data)	March 31, 2011		June 30, 2011		Sept. 30, 2011		Dec. 31, 2011
Operating revenues	$	2,816,540	$	2,438,222	$	2,831,598	$	2,568,410
Operating income		426,663		359,442		651,496		344,001
Income from continuing operations		203,467		158,671		338,295		140,941
Discontinued operations - income (loss)		102		91		37		(432	)
Net income		203,569		158,762		338,332		140,509
Earnings available to common shareholders		202,509		157,702		333,658		140,509
Earnings per share total - basic	$	0.42	$	0.33	$	0.69	$	0.29
Earnings per share total - diluted		0.42		0.33		0.69		0.29
Cash dividends declared per common share		0.25		0.26		0.26		0.26

	Quarter Ended
(Amounts in thousands, except per share data)	March 31, 2010			June 30, 2010		Sept. 30, 2010			Dec. 31, 2010
Operating revenues	$	2,807,462		$	2,307,764	$	2,628,787		$	2,566,934
Operating income		403,665			325,304		568,630			322,370
Income from continuing operations		167,340			135,625		312,488			136,503
Discontinued operations - income (loss)		(222	)		4,151		(182	)		131
Net income		167,118			139,776		312,306			136,634
Earnings available to common shareholders		166,058			138,716		311,246			135,573
Earnings per share total - basic	$	0.36		$	0.30	$	0.68		$	0.29
Earnings per share total - diluted		0.36			0.30		0.67			0.29
Cash dividends declared per common share		0.25			0.25		0.25			0.25