Quarterly Result of Operations (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2015

Selected Quarterly Financial Information [Abstract]

Quarterly Results of Operations (Unaudited)

	First Quarter		Second Quarter		Third Quarter		Fourth Quarter
	(In thousands, except per share data)
2015
Operating revenue	$	1,015,144	$	1,059,404	$	1,064,973	$	1,089,801
Operating income	75,000		98,476		74,921		121,707
Net income	37,840		50,954		36,281		72,502
Basic earnings per share	0.27		0.36		0.25		0.52
Diluted earnings per share	0.26		0.35		0.25		0.51
2014
Operating revenue	$	1,008,446	$	1,075,898	$	1,074,880	$	1,139,500
Operating income	46,170		94,022		97,411		132,467
Net income	12,305		40,198		50,158		58,491
Basic earnings per share	0.09		0.28		0.35		0.41
Diluted earnings per share	0.09		0.28		0.35		0.41