Summarized Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2015

Quarterly Financial Information Disclosure [Abstract]

Summarized Quarterly Financial Data (Unaudited)

	Quarter Ended
(Amounts in thousands, except per share data)	March 31, 2015		June 30, 2015		Sept. 30, 2015		Dec. 31, 2015
Operating revenues	$	2,962,219	$	2,515,134	$	2,901,312	$	2,645,821
Operating income	350,845		422,845		785,812		441,010
Net income	152,066		196,931		426,463		209,025
EPS total — basic	$	0.30	$	0.39	$	0.84	$	0.41
EPS total — diluted	0.30		0.39		0.84		0.41
Cash dividends declared per common share	0.32		0.32		0.32		0.32

	Quarter Ended
(Amounts in thousands, except per share data)	March 31, 2014		June 30, 2014		Sept. 30, 2014		Dec. 31, 2014
Operating revenues	$	3,202,604	$	2,685,096	$	2,869,807	$	2,928,628
Operating income	493,992		397,208		665,680		391,250
Net income	261,221		195,164		368,582		196,339
EPS total — basic	$	0.52	$	0.39	$	0.73	$	0.39
EPS total — diluted	0.52		0.39		0.73		0.39
Cash dividends declared per common share	0.30		0.30		0.30		0.30