12. Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Data

Quarter Ended		Operating Revenue		Operating Income		Net Income		Income  Per Basic Share		Income  Per Diluted Share
	(In thousands, except per share amounts)
03/31/17		$	38,504	$	11,327	$	9,950	$	5.42	$	5.36
06/30/17			36,164		10,175		10,026		5.44		5.40
09/30/17			37,903		11,479		7,971		4.30		4.29
12/31/17			34,024		8,293		8,646		4.67		4.66
03/31/16		$	36,215	$	10,465	$	6,945	$	3.81	$	3.76
06/30/16			36,143		10,074		7,450		4.09		4.02
09/30/16			37,835		10,976		7,614		4.17		4.10
12/31/16			33,294		7,611		5,571		3.05		3.00