Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2012

Financial Instruments [Abstract]

Carrying amount and fair value of debt

(Thousands of dollars)
	March 31, 2012				March 31, 2011
	Carrying		Fair		Carrying		Fair
	Amount		Value		Amount		Value
Publicly traded debt	$	632,435	$	701,156	$	632,387	$	666,247
Non-traded debt		12,356		11,860		28,509		26,720