Employee and Retiree Benefit Plans (Tables)

6 Months Ended

Jun. 30, 2016

Employee and Retiree Benefit Plans [Abstract]

Components of Net Periodic Benefit Expense

	Three Months Ended June 30,
	Pension Benefits			Other Postretirement Benefits
(Thousands of dollars)		2016	2015	2016		2015
Service cost	$	2,770	4,772		675		828
Interest cost		8,865	7,971		1,107		1,192
Expected return on plan assets		(9,698)	(8,724)		–		–
Amortization of prior service cost		321	198		(20)		(20)
Amortization of transitional asset		–	274		2		3
Recognized actuarial loss		3,718	3,891		36		190
		5,976	8,382		1,800		2,193
Special termination benefits		–	8,606		–		–
Curtailments		–	306		–		–
Net periodic benefit expense	$	5,976	17,294		1,800		2,193
	Six Months Ended June 30,
	Pension Benefits			Other Postretirement Benefits
(Thousands of dollars)		2016	2015	2016		2015
Service cost	$	5,923	9,853		1,348		1,656
Interest cost		14,473	15,921		2,215		2,384
Expected return on plan assets		(15,083)	(17,411)		–		–
Amortization of prior service cost		640	393		(41)		(41)
Amortization of transitional asset		–	545		2		3
Recognized actuarial loss		7,247	7,782		75		385
		13,200	17,083		3,599		4,387
Special termination benefits		–	8,606		–		–
Curtailments		822	306		(19)		–
Net periodic benefit expense	$	14,022	25,995		3,580		4,387