Employee and Retiree Benefit Plans (Tables)

6 Months Ended

Jun. 30, 2015

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)	2015		2014	2015		2014
Service cost	$	4,772	6,284		828		672
Interest cost		7,971	8,253		1,192		1,277
Expected return on plan assets		(8,724)	(8,528)		–		–
Amortization of prior service cost		198	228		(20)		(20)
Amortization of transitional asset		274	212		3		2
Recognized actuarial loss		3,891	1,733		190		59
		8,382	8,182		2,193		1,990
Special termination benefits		8,606	–		–		–
Curtailments		306	–		–		–
Net periodic benefit expense	$	17,294	8,182		2,193		1,990
	Six Months Ended June 30,
	Pension Benefits			Other Postretirement Benefits
(Thousands of dollars)		2015	2014	2015		2014
Service cost	$	9,853	12,840		1,656		1,344
Interest cost		15,921	16,468		2,384		2,555
Expected return on plan assets		(17,411)	(17,008)		–		–
Amortization of prior service cost		393	453		(41)		(41)
Amortization of transitional asset		545	420		3		3
Recognized actuarial loss		7,782	3,466		385		118
		17,083	16,639		4,387		3,979
Special termination benefits		8,606	–		–		–
Curtailments		306	–		–		–
Net periodic benefit expense	$	25,995	16,639		4,387		3,979