Employee and Retiree Benefit Plans (Tables)

9 Months Ended

Sep. 30, 2015

Employee and Retiree Benefit Plans [Abstract]

Components of Net Periodic Benefit Expense

	Three Months Ended September 30,
	Pension Benefits			Other Postretirement Benefits
(Thousands of dollars)		2015	2014	2015		2014
Service cost	$	5,898	6,208		826		672
Interest cost		8,972	8,239		1,192		1,278
Expected return on plan assets		(10,471)	(8,506)		–		–
Amortization of prior service cost		187	227		(21)		(20)
Amortization of transitional asset		402	208		2		1
Recognized actuarial loss		3,885	1,735		193		59
Net periodic benefit expense	$	8,873	8,111		2,192		1,990
	Nine Months Ended September 30,
	Pension Benefits			Other Postretirement Benefits
(Thousands of dollars)		2015	2014	2015		2014
Service cost	$	15,751	19,048		2,482		2,016
Interest cost		24,893	24,707		3,576		3,833
Expected return on plan assets		(27,882)	(25,514)		–		–
Amortization of prior service cost		580	680		(62)		(61)
Amortization of transitional asset		947	628		5		4
Recognized actuarial loss		11,667	5,201		578		177
		25,956	24,750		6,579		5,969
Special termination benefits		8,606	–		–		–
Curtailments		306	–		–		–
Net periodic benefit expense	$	34,868	24,750		6,579		5,969