12. Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2015

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)
03/31/15	$	38,324	$	11,486	$	7,602	$	4.05	$	4.01
06/30/15		37,655		11,120		7,474		4.04		3.99
09/30/15		37,381		11,573		7,799		4.25		4.19
12/31/15		32,372		8,330		6,050		3.32		3.27
03/31/14	$	36,419	$	10,700	$	7,201	$	3.63	$	3.61
06/30/14		35,025		10,257		6,882		3.51		3.48
09/30/14		36,625		11,226		7,685		3.94		3.91
12/31/14		32,693		8,632		6,040		3.11		3.08