Condensed Consolidated Statements of Changes in Equity (USD $) In Thousands, unless otherwise specified	Common Units	Class B Units	Non-controlling Interest	Total
Balance, Temporary Equity at Dec. 31, 2013				$ 235,617
Balance, Equity at Dec. 31, 2013	3,476,295	602,025	719,813	4,798,133
Balance, Equity (in units) at Dec. 31, 2013	157,766	15,964
Increase (Decrease) in Equity
Issuance of units in public offering, net of offering costs	271,880			271,880
Issuance of units in public offering, net of offering costs (in units)	4,249
Distributions paid	(136,405)		(90)	(136,495)
Redeemable non-controlling interest classified as temporary equity			104,052	104,052
Share-based compensation activity	(2,881)			(2,881)
Share-based compensation activity (in units)	210
Deferred income tax impact from changes in equity	(7,874)			(7,874)
Net (loss) income	12,492		3,424	15,916
Redeemable Non-controlling Interest (Temporary Equity)
Redeemable non-controlling interest classified as temporary equity				(104,052)
Balance, Temporary Equity at Mar. 31, 2014				131,565
Balance, Equity at Mar. 31, 2014	3,613,507	602,025	827,199	5,042,731
Balance, Equity (in units) at Mar. 31, 2014	162,225	15,964
Balance, Equity at Dec. 31, 2014	4,758,243	451,519	983,477	6,193,239
Balance, Equity (in units) at Dec. 31, 2014	186,553	11,973
Increase (Decrease) in Equity
Distributions paid	(168,718)		(9,567)	(178,285)
Contributions from non-controlling interest			19,571	19,571
Sale of equity interest in a joint venture			11,319	11,319
Transfer of interest due to sale of joint venture	4,370		(4,370)
Share-based compensation activity	(194)			(194)
Share-based compensation activity (in units)	198
Deferred income tax impact from changes in equity	(343)			(343)
Net (loss) income	(9,083)		14,604	5,521
Balance, Equity at Mar. 31, 2015	$ 4,584,275	$ 451,519	$ 1,015,034	$ 6,050,828
Balance, Equity (in units) at Mar. 31, 2015	186,751	11,973