Note 11 - Quarterly Financial Information (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2013

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Information [Table Text Block]

	Quarter
	First		Second		Third		Fourth
2013:
Operating revenues	$	1,291,587	$	1,382,858	$	1,435,850	$	1,474,276
Operating income	$	125,039	$	147,407	$	150,729	$	153,533
Net earnings	$	73,349	$	87,697	$	89,472	$	91,864
Basic earnings per share	$	0.62	$	0.75	$	0.76	$	0.78
Diluted earnings per share	$	0.61	$	0.73	$	0.75	$	0.77

2012:
Operating revenues	$	1,165,922	$	1,255,130	$	1,295,792	$	1,338,136
Operating income	$	116,597	$	137,215	$	133,052	$	143,335
Net earnings	$	67,684	$	80,451	$	78,241	$	83,977
Basic earnings per share	$	0.58	$	0.69	$	0.66	$	0.71
Diluted earnings per share	$	0.57	$	0.67	$	0.65	$	0.70