Summarized Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2012

Summarized Quarterly Financial Data (Unaudited) [Abstract]

Summarized Quarterly Financial Data (Unaudited)

15. Summarized Quarterly Financial Data (Unaudited)

	Quarter Ended
(Thousands of Dollars)	March 31, 2012		June 30, 2012		Sept. 30, 2012		Dec. 31, 2012
Operating revenues	$	340,488	$	380,201	$	471,889	$	347,477
Operating income		31,845		61,891		107,509		24,510
Net income		11,360		30,294		58,247		6,468

	Quarter Ended
(Thousands of Dollars)	March 31, 2011		June 30, 2011		Sept. 30, 2011		Dec. 31, 2011
Operating revenues	$	381,209	$	433,289	$	522,921	$	370,146
Operating income		29,499		53,433		92,885		24,780
Net income		10,238		24,672		48,581		6,410

- Definition

The entire disclosure for the quarterly financial data in the annual financial statements. The disclosure may include a tabular presentation of financial information for each fiscal quarter for the current and previous year, including revenues, gross profit, income or loss before extraordinary items and earnings per share data. It also includes an indication if the information in the note is unaudited, comments on the aggregate effect of year-end adjustments, and an explanation of matters or transactions that affect comparability or are pertinent to an understanding of the information furnished.

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