Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Selected Quarterly Financial Data (Unaudited) [Abstract]

Selected Quarterly Financial Data

	First		Second		Third		Fourth		Year
2017
Operating revenues	$	11,290	$	12,254	$	12,692	$	12,353	$	48,589
Operating income		4,857		5,529		6,147		5,940		22,473
Net income		2,581		2,935		3,931		3,527		12,974
Basic earnings per share		0.20		0.23		0.31		0.27		1.01
Diluted earnings per share		0.20		0.23		0.31		0.27		1.01
Dividends declared per share		0.1602		0.1602		0.1602		0.1666		0.6472
2016
Operating revenues	$	11,278	$	11,820	$	12,601	$	11,885	$	47,584
Operating income		5,214		5,695		6,414		5,565		22,888
Net income		2,486		2,847		3,571		2,942		11,846
Basic earnings per share		0.19		0.23		0.27		0.23		0.92
Diluted earnings per share		0.19		0.23		0.27		0.23		0.92
Dividends declared per share		0.1555		0.1555		0.1555		0.1602		0.6267