PARTNERS' CAPITAL AND DISTRIBUTIONS - Distributions to Unitholders (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands															12 Months Ended
	Mar. 01, 2016	Feb. 12, 2016	Nov. 17, 2015	Aug. 17, 2015	May. 18, 2015	Feb. 24, 2015	Nov. 25, 2014	Aug. 25, 2014	May. 19, 2014	Feb. 25, 2014	Nov. 19, 2013	Aug. 20, 2013	May. 31, 2013	Feb. 28, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Distributions to unitholders
Total cash distributions															$ 590,971	$ 527,198	$ 428,829
Limited Partners
Distributions to unitholders
Amount Per LP Unit (in dollars per unit)			$ 1.1750	$ 1.1625	$ 1.1500	$ 1.1375	$ 1.1250	$ 1.1125	$ 1.1000	$ 1.0875	$ 1.0750	$ 1.0625	$ 1.0500	$ 1.0375
Total cash distributions			$ 152,175	$ 149,490	$ 147,085	$ 145,382	$ 143,386	$ 133,142	$ 128,042	$ 125,806	$ 124,051	$ 104,293	$ 102,689	$ 101,475	$ 594,132	$ 530,376	$ 432,508
Limited Partners | Scenario, Forecast
Distributions to unitholders
Total cash distributions	$ 154,400
Limited Partners | Subsequent event
Distributions to unitholders
Cash distributions declared		$ 1.1875
Class B Units
Distributions to unitholders
Units Distributions												145	163	186			494