QUARTERLY FINANCIAL DATA (UNAUDITED) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Data [Abstract]

Schedule of Quarterly Financial Information

The following table summarizes quarterly financial data for the years ended December 31, 2017 and 2016:

	First Quarter		Second Quarter		Third Quarter		Fourth Quarter		Total
	(Thousands of Dollars, Except Per Unit Data)
2017:
Net income	$	16,992	$	51,311	$	11,030	$	7,442	$	86,775
Net income per unit	0.39		1.19		0.26		0.17		2.01
Cash distributions per unit	0.545		0.545		0.545		0.545		2.180
2016:
Net income	$	16,676	$	15,073	$	17,320	$	5,999	$	55,068
Net income per unit	0.39		0.35		0.40		0.14		1.28
Cash distributions per unit	0.545		0.545		0.545		0.545		2.180