Long-Term Debt (Tables)

6 Months Ended

Jun. 30, 2013

Debt Disclosure [Abstract]

Schedule of Estimated Fair Values of Long-Term Debt

The external credit rating, coupon rate, and maturity of each security are considered in the valuation, as applicable.

	June 30, 2013				December 31, 2012
	Carrying Amount		Market Value		Carrying Amount		Market Value
(Thousands of dollars)
Debentures:
Notes, 4.45%, due 2020	$	125,000	$	134,581	$	125,000	$	141,771
Notes, 6.1%, due 2041		125,000		143,655		125,000		165,779
Notes, 3.875%, due 2022		250,000		261,148		250,000		277,950
8% Series, due 2026		75,000		102,116		75,000		111,501
Medium-term notes, 7.59% series, due 2017		25,000		29,442		25,000		30,710
Medium-term notes, 7.78% series, due 2022		25,000		31,998		25,000		34,637
Medium-term notes, 7.92% series, due 2027		25,000		33,398		25,000		36,953
Medium-term notes, 6.76% series, due 2027		7,500		8,976		7,500		10,058
Unamortized discount		(3,320)				(3,403)
		654,180				654,097
Revolving credit facility and commercial paper		119,000		119,000		111,000		111,000
Industrial development revenue bonds:
Variable-rate bonds:
Tax-exempt Series A, due 2028		50,000		50,000		50,000		50,000
2003 Series A, due 2038		50,000		50,000		50,000		50,000
2008 Series A, due 2038		50,000		50,000		50,000		50,000
2009 Series A, due 2039		50,000		50,000		50,000		50,000
Fixed-rate bonds:
5.55% 1999 Series D, due 2038		8,270		8,314		8,270		8,375
5.45% 2003 Series C, due 2038		-		-		30,000		30,152
5.25% 2003 Series D, due 2038		20,000		20,436		20,000		20,571
5.80% 2003 Series E, due 2038		-		-		15,000		15,102
5.25% 2004 Series A, due 2034		65,000		63,500		65,000		66,955
5.00% 2004 Series B, due 2033		31,200		30,300		31,200		31,655
4.85% 2005 Series A, due 2035		100,000		94,660		100,000		101,184
4.75% 2006 Series A, due 2036		24,855		23,588		24,855		25,189
Unamortized discount		(2,854)				(3,195)
		446,471				491,130
NPL credit facility		-		-		41,562		41,562
NPL other debt obligations		47,687		47,454		20,721		20,991
		1,267,338				1,318,510
Less: current maturities		(11,000)				(50,137)
Long-term debt, less current maturities	$	1,256,338			$	1,268,373