Quarterly Financial Information (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2020

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, 2020
Operating revenue	$	166,318	$	160,873	$	162,282	$	155,789
Operating income	17,326		24,989		27,339		23,765
Income before income taxes	17,703		25,146		27,510		23,902
Net income	13,238		19,182		20,714		17,672
Net income per share, basic	0.16		0.24		0.25		0.22
Net income per share, diluted	0.16		0.24		0.25		0.22
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