Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2011

Financial Instruments [Abstract]

Financial Instruments

	September 30, 2011				September 30, 2010
	Carrying		Fair		Carrying		Fair
(Thousands of dollars)	Amount		Value		Amount		Value
Publicly traded debt	$	632,412	$	689,775	$	691,493	$	760,623
Non-traded debt		18,929		18,222		20,293		19,623