Summary of Quarterly Operating Results (unaudited) (Tables)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Summary of Quarterly Operating Results (Unaudited)

(Amounts in thousands, except per share data)

Three months ended, 2018	March 31		June 30		September 30		December 31
Operating revenue	$	392,805	$	428,732	$	425,562	$	406,750
Operating income		27,579		41,565		38,697		33,336
Net income		21,125		30,281		28,195		25,380
Basic earnings per share	$	0.82	$	1.18	$	1.09	$	0.98
Diluted earnings per share	$	0.80	$	1.15	$	1.07	$	0.97
Three months ended, 2017	March 31		June 30		September 30		December 31
Operating revenue	$	323,090	$	364,404	$	357,010	$	360,196
Operating income		17,527		29,686		24,568		22,928
Net income		11,395		17,571		14,373		47,789
Basic earnings per share	$	0.45	$	0.69	$	0.56	$	1.87
Diluted earnings per share	$	0.44	$	0.68	$	0.55	$	1.82