Summary of Quarterly Operating Results (unaudited) (Tables)

12 Months Ended

Dec. 31, 2015

Quarterly Financial Information Disclosure [Abstract]

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