Condensed Consolidated Statements of Changes in Owners' Equity (USD $) In Thousands	Common Unitholders [Member]	Class B Unitholders [Member]	General Partner Interest	Total
Beginning Balance at Dec. 31, 2011	$ 935,425	$ 232	$ (15,618)	$ 920,039
Conversion vested phantom units	2,836			2,836
Proceeds from public equity offering, net of underwriters discount and offering costs of $157	262,676			262,676
Contributions from general partner			5,714	5,714
Distributions	(26,264)	(2,955)	(596)	(29,815)
Equity-based compensation	3,458			3,458
Net (loss) income	25,333	2,688	572	28,593
Ending Balance at Mar. 31, 2012	1,203,464	(35)	(9,928)	1,193,501
Beginning Balance at Dec. 31, 2012	1,072,175		(12,351)	1,059,824
Conversion vested phantom units	2,365			2,365
Contributions from general partner			334	334
Distributions	(33,171)		(667)	(33,838)
Equity-based compensation	4,217		86	4,303
Net (loss) income	(45,649)		(932)	(46,581)
Ending Balance at Mar. 31, 2013	$ 999,937		$ (13,530)	$ 986,407