Condensed Consolidated Statements of Changes in Equity (USD $) In Thousands, unless otherwise specified	Total	Common Units	Class B Units	Non-controlling Interest	Redeemable Noncontrolling Interest (Temporary Equity)
Balance at Dec. 31, 2011	$ 1,395,242	$ 642,522	$ 752,531	$ 189
Balance (in units) at Dec. 31, 2011		94,940	19,954
Increase (Decrease) in Equity
Issuance of units in public offerings, net of offering costs	852,873	852,873
Issuance of units in public offerings, net of offering costs (in units)		15,508
Distributions paid	(155,144)	(155,073)		(71)
Contributions from non-controlling interest	1,101			1,101
Share-based compensation activity	537	537
Share-based compensation activity (in units)		246
Excess tax benefits related to share-based compensation	2,207	2,207
Deferred income tax impact from changes in equity	(42,854)	(42,854)
Net income (loss)	202,307	202,928		(621)
Balance at Jun. 30, 2012	2,256,269	1,503,140	752,531	598
Balance (in units) at Jun. 30, 2012		110,694	19,954
Balance at Dec. 31, 2012	3,111,398	2,097,404	752,531	261,463
Balance (in units) at Dec. 31, 2012		127,494	19,954
Increase (Decrease) in Equity
Issuance of units in public offerings, net of offering costs	348,352	348,352
Issuance of units in public offerings, net of offering costs (in units)	5,700	5,720
Distributions paid	(215,015)	(214,903)		(112)
Contributions from non-controlling interest	685,219			685,219
Redeemable non-controlling interest classified as temporary equity	(486,670)			(486,670)	486,670
Share-based compensation activity	2,092	2,092
Share-based compensation activity (in units)		161
Excess tax benefits related to share-based compensation	650	650
Deferred income tax impact from changes in equity	(28,077)	(28,077)
Net income (loss)	64,367	68,241		(3,874)
Balance at Jun. 30, 2013					486,670
Balance at Jun. 30, 2013	$ 3,482,316	$ 2,273,759	$ 752,531	$ 456,026
Balance (in units) at Jun. 30, 2013		133,375	19,954