Net periodic benefit cost, some of which is capitalized as a component of labor cost and some of which is deferred as a regulatory asset, is comprised of the following components and is shown for our noncontributory defined benefit pension plan, our supplemental retirement program (SERP) and other postretirement benefits (OPEB) (in thousands):

	Three months ended September 30,
	Pension Benefits						SERP						OPEB
	2013			2012			2013			2012			2013			2012
Service cost	$	1,863		$	1,439		$	34		$	23		$	735		$	671
Interest cost	2,516			2,591			78			86			957			962
Expected return on plan assets	(3,107		)	(3,080		)	—			—			(1,088		)	(1,018		)
Amortization of prior service cost (1)	133			133			(2		)	(2		)	(253		)	(253		)
Amortization of net actuarial loss (1)	2,611			2,052			142			139			565			311
Net periodic benefit cost	$	4,016		$	3,135		$	252		$	246		$	916		$	673

	Nine months ended September 30,
	Pension Benefits						SERP						OPEB
	2013			2012			2013			2012			2013			2012
Service cost	$	5,590		$	4,696		$	101		$	39		$	2,206		$	1,801
Interest cost	7,547			7,693			236			197			2,870			3,027
Expected return on plan assets	(9,321		)	(9,232		)	—			—			(3,265		)	(3,101		)
Amortization of prior service cost (1)	399			398			(6		)	(6		)	(758		)	(758		)
Amortization of net actuarial loss (1)	7,834			5,952			426			291			1,696			1,246
Net periodic benefit cost	$	12,049		$	9,507		$	757		$	521		$	2,749		$	2,215

	Twelve months ended September 30,
	Pension Benefits						SERP						OPEB
	2013			2012			2013			2012			2013			2012
Service cost	$	7,156		$	6,094		$	114		$	62		$	2,806		$	2,367
Interest cost	10,111			10,295			301			243			3,879			4,123
Expected return on plan assets	(12,398		)	(12,017		)	—			—			(4,299		)	(4,140		)
Amortization of prior service cost (1)	531			532			(8		)	(8		)	(1,011		)	(1,011		)
Amortization of net actuarial loss (1)	9,818			7,325			523			334			2,112			1,687
Net periodic benefit cost	$	15,218		$	12,229		$	930		$	631		$	3,487		$	3,026

(1) Amounts are amortized from our regulatory asset originally recorded upon recognizing our net pension liability on the balance sheet.