EMPLOYEE BENEFIT PLANS (Notes)

6 Months Ended

Jun. 30, 2017

Employee Benefit Plans [Line Items]

EMPLOYEE BENEFIT PLANS

8. EMPLOYEE BENEFIT PLANS

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

	Pension Benefits
	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2017			2016			2017			2016
	(Thousands of dollars)
Components of net periodic benefit cost
Service cost	$	3,044		$	3,014		$	6,088		$	6,028
Interest cost	10,113			11,388			20,226			22,775
Expected return on assets	(14,624		)	(15,296		)	(29,248		)	(30,592		)
Amortization of net loss	9,027			8,885			18,054			17,771
Net periodic benefit cost	$	7,560		$	7,991		$	15,120		$	15,982

	Other Postemployment Benefits
	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2017			2016			2017			2016
	(Thousands of dollars)
Components of net periodic benefit cost
Service cost	$	627		$	638		$	1,254		$	1,276
Interest cost	2,472			2,627			4,944			5,254
Expected return on assets	(3,147		)	(3,071		)	(6,294		)	(6,142		)
Amortization of unrecognized prior service cost	(1,149		)	(908		)	(2,298		)	(1,816		)
Amortization of net loss	1,621			1,151			3,242			2,302
Net periodic benefit cost	$	424		$	437		$	848		$	874

We recover qualified pension benefit plan and other postemployment 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 authorized by the applicable utility commission. Regulatory deferrals related to net periodic benefit cost were not material for the three and six months ended June 30, 2017.