Employee and Retiree Benefit Plans (Tables)

3 Months Ended

Mar. 31, 2016

Employee and Retiree Benefit Plans [Abstract]

Components of Net Periodic Benefit Expense

	Three Months Ended March 31,
	Pension Benefits			Other Postretirement Benefits
(Thousands of dollars)		2016	2015	2016		2015
Service cost	$	3,153	5,081		673		828
Interest cost		5,608	7,950		1,108		1,192
Expected return on plan assets		(5,385)	(8,687)		–		–
Amortization of prior service cost		319	195		(21)		(21)
Amortization of transitional asset		–	271		–		–
Recognized actuarial loss		3,529	3,891		39		195
Curtailments		822	–		(19)		–
Net periodic benefit expense	$	8,046	8,701		1,780		2,194