Summary of Quarterly Operating Results (unaudited)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Summary of Quarterly Operating Results (unaudited)

10.    Summary of Quarterly Operating Results (unaudited)

(Amounts in thousands, except per share data)

Three months ended, 2017	March 31		June 30		September 30		December 31
Operating revenue	$	317,037	$	358,160	$	350,062	$	353,251
Operating income		17,519		29,718		24,602		22,898
Net income		11,387		17,603		14,407		47,759
Basic earnings per share	$	0.45	$	0.69	$	0.56	$	1.87
Diluted earnings per share	$	0.44	$	0.68	$	0.55	$	1.82
Three months ended, 2016	March 31		June 30		September 30		December 31
Operating revenue	$	289,911	$	311,905	$	316,442	$	300,223
Operating income		17,584		21,721		22,644		17,187
Net income		10,575		13,275		13,826		10,348
Basic earnings per share	$	0.42	$	0.53	$	0.55	$	0.41
Diluted earnings per share	$	0.42	$	0.52	$	0.54	$	0.40