CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Units	Class B Units	Non-controlling Interest	Redeemable Non-Controlling Interest (Temporary Equity)
Balance at Dec. 31, 2010	$ 1,350,294	$ 957,452		$ 392,842
Balance (in units) at Dec. 31, 2010		71,440,000
Increase (Decrease) in Equity
Issuance of units in public equity offerings, net of offering costs	1,095,488	1,095,488
Issuance of units in public equity offerings, net of offering costs (in units)		23,225,000
Issuance of Class B units	752,531		752,531
Issuance of Class B units (in units)			19,954,000
Distributions paid	(281,203)	(218,398)		(62,805)
Contributions from non-controlling interest	126,392			126,392
Purchase of non-controlling interest of MarkWest Liberty M&R, net of tax benefit	(1,698,810)	(1,198,465)		(500,345)
Share-based compensation activity	8,083	8,083
Share-based compensation activity (in units)		275,000
Excess tax benefits related to share-based compensation	1,084	1,084
Deferred income tax impact from changes in equity	(63,417)	(63,417)
Net income (loss)	104,800	60,695		44,105
Balance at Dec. 31, 2011	1,395,242	642,522	752,531	189
Balance (in units) at Dec. 31, 2011		94,940,000	19,954,000
Increase (Decrease) in Equity
Issuance of units in public equity offerings, net of offering costs	1,634,081	1,634,081
Issuance of units in public equity offerings, net of offering costs (in units)		32,308,000
Distributions paid	(340,038)	(339,967)		(71)
Contributions from non-controlling interest	264,782			264,782
Share-based compensation activity	6,548	6,548
Share-based compensation activity (in units)		246,000
Excess tax benefits related to share-based compensation	907	907
Deferred income tax impact from changes in equity	(67,089)	(67,089)
Net income (loss)	216,965	220,402		(3,437)
Balance at Dec. 31, 2012	3,111,398	2,097,404	752,531	261,463
Balance (in units) at Dec. 31, 2012		127,494,000	19,954,000
Increase (Decrease) in Equity
Issuance of units in public equity offerings, net of offering costs	1,698,066	1,698,066
Issuance of units in public equity offerings, net of offering costs (in units)		26,115,000
Conversion of Class B units to common units		150,506	(150,506)
Conversion of Class B units to common units (in units)		3,990,000	(3,990,000)
Distributions paid	(462,699)	(462,488)		(211)
Contributions from non-controlling interest	685,219			685,219
Redeemable non-controlling interest classified as temporary equity	(235,617)			(235,617)	235,617
Share-based compensation activity	11,072	11,072
Share-based compensation activity (in units)		167,000
Other	6,591			6,591
Deferred income tax impact from changes in equity	(56,342)	(56,342)
Net income (loss)	40,445	38,077		2,368
Balance at Dec. 31, 2013	235,617
Balance at Dec. 31, 2013	$ 4,798,133	$ 3,476,295	$ 602,025	$ 719,813	$ 235,617
Balance (in units) at Dec. 31, 2013		157,766,000	15,964,000