Summary of Quarterly Operating Results (unaudited)

12 Months Ended

Dec. 31, 2015

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, 2015	March 31		June 30		September 30		December 31
Operating revenue	$	293,022	$	323,480	$	317,199	$	287,610
Operating income		21,233		31,281		19,845		17,616
Net income		12,605		19,247		11,777		11,387
Basic earnings per share	$	0.51	$	0.77	$	0.47	$	0.46
Diluted earnings per share	$	0.49	$	0.75	$	0.46	$	0.46
Three months ended, 2014	March 31		June 30		September 30		December 31
Operating revenue	$	299,730	$	330,399	$	332,544	$	309,648
Operating income		15,231		22,741		27,149		20,572
Net income		8,576		13,568		16,278		13,569
Basic earnings per share	$	0.35	$	0.55	$	0.66	$	0.55
Diluted earnings per share	$	0.34	$	0.53	$	0.64	$	0.53