Employee and Retiree Benefit Plans (Tables)

9 Months Ended

Sep. 30, 2016

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)		2016	2015	2016		2015
Service cost	$	2,610	5,898		674		826
Interest cost		5,913	8,972		1,109		1,192
Expected return on plan assets		(6,626)	(10,471)		–		–
Amortization of prior service cost		323	187		(21)		(21)
Amortization of transitional asset		–	402		2		2
Recognized actuarial loss		3,617	3,885		38		193
Net periodic benefit expense	$	5,837	8,873		1,802		2,192
	Nine Months Ended September 30,
	Pension Benefits			Other Postretirement Benefits
(Thousands of dollars)		2016	2015	2016		2015
Service cost	$	8,533	15,751		2,022		2,482
Interest cost		20,386	24,893		3,324		3,576
Expected return on plan assets		(21,709)	(27,882)		–		–
Amortization of prior service cost		963	580		(62)		(62)
Amortization of transitional asset		–	947		4		5
Recognized actuarial loss		10,864	11,667		113		578
		19,037	25,956		5,401		6,579
Special termination benefits		–	8,606		(19)		–
Curtailments		822	306		–		–
Net periodic benefit expense	$	19,859	34,868		5,382		6,579