EMPLOYEE BENEFIT PLANS (Notes)

3 Months Ended

Mar. 31, 2015

Employee Benefit Plans [Line Items]

EMPLOYEE BENEFIT PLANS

7. EMPLOYEE BENEFIT PLANS

The following tables set forth the components of net periodic benefit cost for our pension and other postretirement benefit plans for the periods indicated:

	Pension Benefits
	Three Months Ended			Three Months Ended
	March 31,			March 31,
	2015			2014
	(Thousands of dollars)
Components of net periodic benefit cost
Service cost	$	3,524		$	2,768
Interest cost	10,652			10,948
Expected return on assets	(15,362		)	(14,965		)
Amortization of unrecognized prior service cost	67			137
Amortization of net loss	11,055			7,550
Net periodic benefit cost	$	9,936		$	6,438

	Other Postretirement Benefits
	Three Months Ended			Three Months Ended
	March 31,			March 31,
	2015			2014
	(Thousands of dollars)
Components of net periodic benefit cost
Service cost	$	849		$	1,174
Interest cost	2,666			2,901
Expected return on assets	(2,908		)	(2,848		)
Amortization of unrecognized prior service cost	(440		)	(440		)
Amortization of net loss	1,510			992
Net periodic benefit cost	$	1,677		$	1,779

We recover qualified pension benefit plan and other postretirement benefit plan costs through rates charged to our customers. Certain utility commissions require that the recovery of these costs be based on specific guidelines. The difference between these regulatory-based amounts and the periodic benefit cost calculated pursuant to GAAP is deferred as a regulatory asset or liability and amortized to expense over periods in which this difference will be recovered in rates, as promulgated by the applicable utility commission. Regulatory adjustments to the net periodic benefit cost were not material for the three month periods ended March 31, 2015 and 2014.