QUARTERLY FINANCIAL DATA (UNAUDITED) (Tables)

12 Months Ended

Dec. 31, 2014

Schedule of Quarterly Financial Information [Line Items]

Quarterly Financial Data

	First Quarter		Second Quarter		Third Quarter		Fourth Quarter
Year Ended December 31, 2014
	(Thousands of dollars)
Revenues	$	766,178	$	296,838	$	241,522	$	514,368
Net margin	$	259,836	$	176,493	$	166,452	$	224,176
Operating income	$	109,353	$	26,812	$	19,119	$	70,010
Net income	$	59,076	$	9,454	$	4,653	$	36,607
Earnings per share
Basic	$	1.13	$	0.18	$	0.09	$	0.70
Diluted	$	1.13	$	0.18	$	0.09	$	0.69

	First Quarter		Second Quarter		Third Quarter		Fourth Quarter
Year Ended December 31, 2013
	(Thousands of dollars)
Revenues	$	635,933	$	311,608	$	219,725	$	522,686
Net margin	$	251,674	$	178,447	$	159,233	$	223,654
Operating income	$	101,838	$	39,307	$	14,189	$	65,014
Net income	$	53,492	$	14,951	$	434	$	30,318
Earnings per share
Basic and diluted	$	1.02	$	0.29	$	0.01	$	0.58