CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash flows from operating activities:
Net income (loss)	$ 106,245	$ 31,102	$ (113,354)
Adjustments to reconcile net income (loss) to net cash provided by operating activities (net of acquisitions):
Depreciation	149,954	123,198	95,537
Amortization of intangible assets	43,617	40,833	40,831
Impairment of goodwill and long-lived assets			5,855
Loss on redemption of debt	78,996	46,326
Amortization of deferred financing costs and discount	5,114	10,264	9,718
Accretion of asset retirement obligations	1,190	237	198
Amortization of deferred contract cost	312	312	312
Phantom unit compensation expense	13,479	15,319	7,448
Loss (earnings) of unconsolidated affiliates	1,095	(1,562)	(3,505)
Gain on sale of unconsolidated affiliate			(6,801)
Contribution to unconsolidated affiliate	(560)
Distributions from unconsolidated affiliate	300	2,508
Unrealized loss on derivative instruments	4,147	28,475	227,920
Loss on disposal of property, plant and equipment	8,797	3,149	1,677
Deferred income taxes	(3,929)	(4,466)	(50,088)
Other	1,626		(2,228)
Changes in operating assets and liabilities, net of working capital acquired:
Receivables	(45,463)	(37,090)	(33,133)
Inventories	(16,025)	5,710	6,245
Other current assets	(3,728)	2,654	1,074
Accounts payable and accrued liabilities	54,745	45,361	30,717
Other long-term assets	(307)	174	(2,808)
Other long-term liabilities	15,093	(176)	7,486
Net cash provided by operating activities	414,698	312,328	223,101
Cash flows from investing activities:
Restricted cash	2,006	(28,001)
Capital expenditures	(551,281)	(458,668)	(486,623)
Acquisition of business	(230,728)
Equity investments			(405)
Proceeds from sale of unconsolidated affiliate			25,000
Proceeds from disposal of property, plant and equipment	3,450	733	275
Net cash flows used in investing activities	(776,553)	(485,936)	(461,753)
Cash flows from financing activities:
Proceeds from revolving credit facility	1,182,200	494,404	725,200
Payments of revolving credit facility	(1,116,200)	(553,704)	(850,600)
Proceeds from long-term debt	1,199,000	500,000	117,000
Payments of long-term debt	(693,888)	(375,000)
Payments of premiums on redemption of long-term debt	(71,377)	(9,732)
Payments for debt issuance costs, deferred financing costs and registration costs	(20,163)	(20,912)	(8,554)
Acquisition of non-controlling interest, including transaction costs	(997,601)
Contributions to MarkWest Liberty Midstream joint venture, net	126,392	158,293	194,536
Proceeds from sale of equity interest in joint venture, net			60,654
Payments of SMR Liability	(1,875)	(1,354)
Proceeds from SMR Transaction			73,129
Proceeds from public equity offerings, net	1,095,488	142,255	178,565
Cash paid for taxes related to net settlement of share-based payment awards	(6,354)	(3,834)	(1,385)
Excess tax benefits related to share-based compensation	1,084	98
Payment of distributions to common unitholders	(218,398)	(181,058)	(155,307)
Payment of distributions to non-controlling interest	(66,887)	(6,150)	(155)
Net cash flows provided by financing activities	411,421	143,306	333,083
Net increase (decrease) in cash and cash equivalents	49,566	(30,302)	94,431
Cash and cash equivalents at beginning of year	67,450	97,752	3,321
Cash and cash equivalents at end of year	$ 117,016	$ 67,450	$ 97,752