Employee and Retiree Benefit Plans (Tables)

3 Months Ended

Mar. 31, 2015

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)		2015	2014	2015		2014
Service cost	$	5,081	6,556		828		672
Interest cost		7,950	8,215		1,192		1,278
Expected return on plan assets		(8,687)	(8,480)		–		–
Amortization of prior service cost		195	225		(21)		(21)
Amortization of transitional asset		271	208		–		1
Recognized actuarial loss		3,891	1,733		195		59
Net periodic benefit expense	$	8,701	8,457		2,194		1,989