Supplemental Condensed Consolidating Financial Information (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010	Dec. 31, 2009
Current assets:
Cash and cash equivalents	$ 95,035	$ 67,450	$ 134,871	$ 97,752
Receivables and other current assets	243,686	226,751
Fair value of derivative instruments	2,835	4,345
Total current assets	341,556	298,546
Total property, plant and equipment, net	2,603,842	2,319,024
Other long-term assets:
Restricted cash	28,100	28,001
Investment in unconsolidated affiliate	27,633	28,688
Intangibles, net of accumulated amortization	625,737	613,578
Fair value of derivative instruments	3,349	417
Other long-term assets	104,808	45,108
Total assets	3,735,025	3,333,362
Current liabilities:
Fair value of derivative instruments	78,345	65,489
Other current liabilities	288,397	276,353
Total current liabilities	366,742	341,842
Deferred income taxes	6,860	10,427
Fair value of derivative instruments	81,121	66,290
Long-term debt, net of discounts	1,582,102	1,273,434
Other long-term liabilities	115,798	105,349
Equity:
MarkWest Energy Partners, L.P. partners' capital	1,106,950	1,070,503	1,237,370
Non-controlling interest in consolidated subsidiaries	475,452	465,517	411,826
Total equity	1,582,402	1,536,020	1,649,196	1,379,393
Total liabilities and equity	3,735,025	3,333,362
Parent
Current assets:
Cash and cash equivalents	3
Receivables and other current assets	846	1,708
Intercompany receivables	1,667,583	1,440,302
Total current assets	1,668,432	1,442,010
Total property, plant and equipment, net	4,379	4,623
Other long-term assets:
Investment in consolidated affiliates	825,036	716,673
Intercompany notes receivable	215,160	197,710
Other long-term assets	33,657	32,587
Total assets	2,746,664	2,393,603
Current liabilities:
Intercompany payables	9,217	672
Other current liabilities	29,173	31,882
Total current liabilities	38,390	32,554
Deferred income taxes	1,606	2,533
Long-term debt, net of discounts	1,582,102	1,273,434
Other long-term liabilities	3,412	3,319
Equity:
MarkWest Energy Partners, L.P. partners' capital	1,121,154	1,081,763
Total equity	1,121,154	1,081,763
Total liabilities and equity	2,746,664	2,393,603
Guarantor Subsidiaries
Current assets:
Cash and cash equivalents	71,584	63,850	54,868	74,448
Receivables and other current assets	216,623	172,209
Intercompany receivables	9,237	1,099
Fair value of derivative instruments	2,835	4,345
Total current assets	300,279	241,503
Total property, plant and equipment, net	1,657,181	1,512,763
Other long-term assets:
Investment in unconsolidated affiliate	27,633	28,688
Investment in consolidated affiliates	482,222	368,864
Intangibles, net of accumulated amortization	625,177	613,000
Fair value of derivative instruments	3,349	417
Other long-term assets	70,780	12,139
Total assets	3,166,621	2,777,374
Current liabilities:
Intercompany payables	1,677,066	1,447,799
Fair value of derivative instruments	78,345	65,489
Other current liabilities	195,445	173,667
Total current liabilities	1,950,856	1,686,955
Deferred income taxes	5,254	7,894
Intercompany notes payable	192,160	197,710
Fair value of derivative instruments	81,121	66,290
Other long-term liabilities	112,194	101,852
Equity:
MarkWest Energy Partners, L.P. partners' capital	825,036	716,673
Total equity	825,036	716,673
Total liabilities and equity	3,166,621	2,777,374
Non-Guarantor Subsidiaries
Current assets:
Cash and cash equivalents	23,448	3,600	80,003	23,304
Receivables and other current assets	26,217	52,834
Intercompany receivables	9,688	7,635
Total current assets	59,353	64,069
Total property, plant and equipment, net	956,486	812,898
Other long-term assets:
Restricted cash	28,100	28,001
Intangibles, net of accumulated amortization	560	578
Other long-term assets	371	382
Total assets	1,044,870	905,928
Current liabilities:
Intercompany payables	225	565
Other current liabilities	63,779	70,804
Total current liabilities	64,004	71,369
Intercompany notes payable	23,000
Other long-term liabilities	192	178
Equity:
MarkWest Energy Partners, L.P. partners' capital	957,674	834,381
Total equity	957,674	834,381
Total liabilities and equity	1,044,870	905,928
Consolidating Adjustments
Current assets:
Intercompany receivables	(1,686,508)	(1,449,036)
Total current assets	(1,686,508)	(1,449,036)
Total property, plant and equipment, net	(14,204)	(11,260)
Other long-term assets:
Investment in consolidated affiliates	(1,307,258)	(1,085,537)
Intercompany notes receivable	(215,160)	(197,710)
Total assets	(3,223,130)	(2,743,543)
Current liabilities:
Intercompany payables	(1,686,508)	(1,449,036)
Total current liabilities	(1,686,508)	(1,449,036)
Intercompany notes payable	(215,160)	(197,710)
Equity:
MarkWest Energy Partners, L.P. partners' capital	(1,796,914)	(1,562,314)
Non-controlling interest in consolidated subsidiaries	475,452	465,517	411,826
Total equity	(1,321,462)	(1,096,797)
Total liabilities and equity	$ (3,223,130)	$ (2,743,543)