Receivables (Tables)

12 Months Ended

Dec. 31, 2011

Receivables [Abstract]

Summary of the Company's receivable balances

The following is a summary of the Company's receivable balances at December 31:

(Thousands of dollars)	2011			2010
Accounts receivable	$	214,608		$	126,671
Notes receivable		16			139
Other receivables		2,108			748
Gross receivables		216,732			127,558
Allowance for doubtful accounts receivable		(125	)		(260	)
Net receivables	$	216,607		$	127,298