Summary of Quarterly Operating Results (unaudited)

12 Months Ended

Dec. 31, 2016

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, 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