Summary of Quarterly Operating Results (unaudited) (Tables)

12 Months Ended

Dec. 31, 2016

Quarterly Financial Information Disclosure [Abstract]

Summary of Quarterly Operating Results (Unaudited)

(Amounts in thousands, except per share data)

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
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	$	0.45