PARTNERS' CAPITAL (Cash Distributions) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	0 Months Ended						3 Months Ended		6 Months Ended		0 Months Ended
	May 15, 2014	Feb. 14, 2014	Nov. 14, 2013	Aug. 14, 2013	May 15, 2013	Feb. 14, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jul. 24, 2014 Subsequent Event	May 15, 2014 General partner	Feb. 14, 2014 General partner	Nov. 14, 2013 General partner	Aug. 14, 2013 General partner	May 15, 2013 General partner	Feb. 14, 2013 General partner	May 15, 2014 Limited partners, Common	Feb. 14, 2014 Limited partners, Common	Nov. 14, 2013 Limited partners, Common	Aug. 14, 2013 Limited partners, Common	May 15, 2013 Limited partners, Common	Feb. 14, 2013 Limited partners, Common	May 15, 2014 Subordinated	Feb. 14, 2014 Subordinated	Nov. 14, 2013 Subordinated	Aug. 14, 2013 Subordinated	May 15, 2013 Subordinated	Feb. 14, 2013 Subordinated	May 15, 2014 General Partner Units	Feb. 14, 2014 General Partner Units	Nov. 14, 2013 General Partner Units	Aug. 14, 2013 General Partner Units	May 15, 2013 General Partner Units	Feb. 14, 2013 General Partner Units
Distribution Made to Limited Partner [Line Items]
Per-unit distribution (in dollars per unit)	$ 0.5	$ 0.48	$ 0.46	$ 0.435	$ 0.42	$ 0.41	$ 0.5	$ 0.42	$ 0.98	$ 0.83	$ 0.52
Distributions to unitholders	$ 30,384	$ 26,366	$ 25,108	$ 23,740	$ 20,923	$ 20,425			$ 56,749	$ 41,348								$ 17,211	$ 13,958	$ 13,377	$ 12,647	$ 10,253	$ 10,009	$ 12,205	$ 11,717	$ 11,229	$ 10,618	$ 10,252	$ 10,008	$ 608	$ 528	$ 502	$ 475	$ 418	$ 408
General partner's IDRs												$ 360	$ 163	$ 0	$ 0	$ 0	$ 0