Employee Benefit Plans: (Tables)

3 Months Ended

Mar. 31, 2013

Employee Benefit Plans:

Schedule of components of net periodic benefit costs, before allocation to the overhead pool, for Registrant's pension plan, postretirement plan, and SERP

	Pension Benefits						Other Postretirement Benefits						SERP
(dollars in thousands)	2013			2012			2013			2012			2013		2012
Components of Net Periodic Benefits Cost:
Service cost	$	1,864		$	1,719		$	106		$	112		$	201	$	183
Interest cost	1,731			1,676			113			136			129		122
Expected return on plan assets	(1,893		)	(1,636		)	(95		)	(90		)	—		—
Amortization of transition	—			—			105			105			—		—
Amortization of prior service cost (benefit)	30			30			(50		)	(50		)	40		40
Amortization of actuarial loss	711			778			—			—			85		77
Net periodic pension cost under accounting standards	2,443			2,567			179			213			455		422
Regulatory adjustment — deferred	(510		)	(566		)	—			—			—		—
Total expense recognized, before allocation to overhead pool	$	1,933		$	2,001		$	179		$	213		$	455	$	422