Quarterly Historical Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2015

Selected Quarterly Financial Information [Abstract]

Schedule of Quarterly Financial Information

The following table sets forth selected unaudited historical operating results data for each quarter (in thousands):

	First Quarter		Second Quarter		Third Quarter		Fourth Quarter
2015
Operating revenues	$	70,283	$	68,038	$	72,111	$	67,432
Operating income	$	21,490	$	21,143	$	23,456	$	21,825
Net income	$	10,403	$	10,547	$	12,287	$	11,937
2014
Operating revenues	$	71,267	$	60,741	$	67,729	$	68,751
Operating income	$	17,546	$	13,782	$	19,007	$	18,779
Net income	$	8,643	$	6,230	$	9,916	$	8,773