Employee and Retiree Benefit Plans (Tables)

6 Months Ended

Jun. 30, 2013

Compensation And Retirement Disclosure [Abstract]

Components of Net Periodic Benefit Expense

The table that follows provides the components of net periodic benefit expense for the three-month and six-month periods ended June 30, 2013 and 2012.

	Three Months Ended June 30,
							Other
	Pension Benefits						Postretirement Benefits
(Thousands of dollars)	2013			2012			2013			2012
Service cost	$	7,094			6,035			1,230			1,049
Interest cost		7,700			7,545			1,279			1,342
Expected return on plan assets		(7,569	)		(6,520	)		0			0
Amortization of prior service cost		303			313			(44	)		(43	)
Amortization of transitional asset		121			116			2			2
Recognized actuarial loss		4,759			3,847			473			452
Special termination benefits		0			6,170			0			0
Net periodic benefit expense	$	12,408			17,506			2,940			2,802
	Six Months Ended June 30,
							Other
	Pension Benefits						Postretirement Benefits
(Thousands of dollars)	2013			2012			2013			2012
Service cost	$	14,697			11,923			2,397			2,090
Interest cost		14,131			14,837			2,513			2,791
Expected return on plan assets		(13,269	)		(12,825	)		0			0
Amortization of prior service cost		579			625			(86	)		(89	)
Amortization of transitional asset		241			227			4			4
Recognized actuarial loss		8,291			7,614			930			941
Special termination benefits		0			6,170			0			0
Net periodic benefit expense	$	24,670			28,571			5,758			5,737