QUARTERLY FINANCIAL DATA (UNAUDITED) (Tables)

12 Months Ended

Dec. 31, 2012

QUARTERLY FINANCIAL DATA (UNAUDITED) [Abstract]

Schedule of Quarterly Financial Information [Table Text Block]

	First Quarter		Second Quarter			Third Quarter		Fourth Quarter		Total
	(Thousands of Dollars, Except Per Unit Data)
2012:
Net income (loss)	$	11,046	$	(33,208	)	$	19,165	$	5,125	$	2,128
Basic and diluted net income (loss) per unit	0.26		(0.78		)	0.45		0.12		0.05
Cash distributions per unit applicable to limited partners	0.510		0.510			0.545		0.545		2.110
2011:
Net income	$	10,183	$	22,061		$	18,362	$	19,030	$	69,636
Basic and diluted net income per unit	0.24		0.52			0.43		0.45		1.64
Cash distributions per unit applicable to limited partners	0.480		0.495			0.495		0.510		1.980