Components of Net Periodic Benefit Cost (Tables)

9 Months Ended

Sep. 30, 2015

Text Block [Abstract]

Schedule of Components of Net Periodic Benefit Costs

As a result, net periodic benefit costs become components of various accounts, primarily operations and maintenance expense, net utility plant, and deferred charges and other assets.

	Qualified Retirement Plan
	Period Ended September 30,
	Three Months						Nine Months						Twelve Months
	2015			2014			2015			2014			2015			2014
(Thousands of dollars)
Service cost	$	6,281		$	5,340		$	18,842		$	16,020		$	24,182		$	21,784
Interest cost		11,057			10,860			33,172			32,581			44,031			41,983
Expected return on plan assets		(14,452	)		(13,336	)		(43,356	)		(40,007	)		(56,691	)		(52,467	)
Amortization of net actuarial loss		8,186			5,718			24,557			17,154			30,276			25,219
Net periodic benefit cost	$	11,072		$	8,582		$	33,215		$	25,748		$	41,798		$	36,519
	SERP
	Period Ended September 30,
	Three Months						Nine Months						Twelve Months
	2015			2014			2015			2014			2015			2014
(Thousands of dollars)
Service cost	$	80		$	73		$	240		$	219		$	313		$	312
Interest cost		424			436			1,271			1,308			1,708			1,692
Amortization of net actuarial loss		323			196			970			588			1,165			830
Net periodic benefit cost	$	827		$	705		$	2,481		$	2,115		$	3,186		$	2,834
	PBOP
	Period Ended September 30,
	Three Months						Nine Months						Twelve Months
	2015			2014			2015			2014			2015			2014
(Thousands of dollars)
Service cost	$	410		$	275		$	1,231		$	826		$	1,506		$	1,131
Interest cost		750			707			2,249			2,122			2,956			2,743
Expected return on plan assets		(866	)		(816	)		(2,598	)		(2,448	)		(3,414	)		(3,154	)
Amortization of prior service costs		334			89			1,001			266			1,090			355
Amortization of net actuarial loss		86			—			259			—			259			236
Net periodic benefit cost	$	714		$	255		$	2,142		$	766		$	2,397		$	1,311