Quarterly financial data (unaudited):

12 Months Ended

Dec. 31, 2015

Quarterly financial data (unaudited):

Quarterly financial data (unaudited):

14. Quarterly financial data (unaudited):

    Summarized quarterly financial information for 2015 and 2014 is as follows:

		First Quarter		Second Quarter		Third Quarter		Fourth Quarter
		(dollars in thousands)
2015
Operating revenues	$	339,778	$	343,741	$	368,664	$	297,642
Operating margin		68,260		63,494		69,287		56,417
Net margin		15,369		10,852		15,908		6,212
2014
Operating revenues	$	367,300	$	355,983	$	369,405	$	315,475
Operating margin		69,857		69,600		70,685		49,255
Net margin		19,223		17,196		14,453		(4,237	)

    The decrease in net margin in the fourth quarter of 2015 and the negative net margins in the fourth quarter of 2014 were due to reductions to revenue requirements in order to achieve the targeted margins for interest ratio of 1.14.