Quarterly Results of Operations (Tables)

12 Months Ended

Dec. 31, 2016

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Results of Operations

(In thousands, except per share amounts)	First Quarter		Second Quarter		Third Quarter		Fourth Quarter
2016:
Operating revenues	$	482,802	$	498,681	$	508,676	$	518,832
Operating income	32,487		29,553		29,074		34,956
Net income	20,092		18,306		18,920		21,811
Basic earnings per share	0.28		0.25		0.26		0.30
Diluted earnings per share	0.28		0.25		0.26		0.30

(In thousands, except per share amounts)	First Quarter		Second Quarter		Third Quarter		Fourth Quarter
2015:
Operating revenues	$	495,654	$	534,644	$	534,448	$	528,783
Operating income	38,185		52,210		52,800		57,261
Net income	23,142		31,848		32,076		36,648
Basic earnings per share	0.32		0.44		0.45		0.51
Diluted earnings per share	0.32		0.44		0.44		0.51