MEMBERS' EQUITY Narrative (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Distributions (dates and totals)
Total cash distributions, paid	$ (23,223)	$ (23,200)	$ (21,708)
Cash distributions per unit, paid		$ 0.545
Cash distributions, payment date	May 15, 2013	Feb. 19, 2013
Total cash distributions, earned	$ 23,222		$ 21,720
Cash distributions per unit, declared	$ 0.545		$ 0.510
Cash distributions, record date	May 06, 2013