Quarterly financial data (unaudited)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Data [Abstract]

Quarterly financial data (unaudited)

Quarterly financial data (unaudited):

Summarized quarterly financial information for 2019 and 2018 is as follows:

	First Quarter		Second Quarter		Third Quarter		Fourth Quarter
	(dollars in thousands)
2019
Operating revenues	$	356,600	$	358,860	$	382,623	$	332,209
Operating margin	66,032		51,712		59,209		40,256
Net margin	23,596		9,383		18,286		3,196
2018
Operating revenues	$	373,646	$	365,921	$	384,644	$	355,902
Operating margin	69,931		60,849		54,845		39,351
Net margin	27,400		17,285		11,334		(4,820)

The negative net margins in the fourth quarter of 2018 were due to reductions to revenue requirements in order to achieve, but not exceed, the targeted margins for interest ratio of 1.14.