Quarterly Financial Information (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information (Unaudited) [Abstract]

Schedule of Quarterly Financial Information [Table Text Block]

	First		Second		Third		Fourth
	(In Thousands, Except Per Share Data)
Year ended December 31, 2019
Operating revenue	$	139,536	$	142,144	$	147,908	$	167,227
Operating income	20,843		29,030		26,739		17,663
Income before income taxes	21,988		30,259		27,415		17,516
Net income	17,318		22,361		20,501		12,787
Net income per share, basic	0.21		0.27		0.25		0.16
Net income per share, diluted	0.21		0.27		0.25		0.16
Year ended December 31, 2018
Operating revenue	$	156,695	$	155,826	$	151,279	$	147,003
Operating income	12,948		22,147		25,132		29,560
Income before income taxes	13,290		22,570		25,718		30,339
Net income	13,378		17,803		19,056		22,440
Net income per share, basic	0.16		0.22		0.23		0.27
Net income per share, diluted	0.16		0.22		0.23		0.27