Represents the period after the end of each quarter within which available cash is distributed to unitholders.

No definition available.

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- Definition

Represents the maximum value of common units representing limited partnership interests that may be sold under a continuous equity offering program.

+ References

No definition available.

+ Details

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Namespace Prefix:	mwe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the maximum number of future fiscal quarters' distributions to unitholders for which cash reserves can be established when determining the cash available for distribution.

+ References

No definition available.

+ Details

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Namespace Prefix:	mwe_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

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- Definition

Date of record for distribution of cash, stock, or units to a member or limited partner of limited liability company (LLC) or limited partnership (LP), in CCYY-MM-DD format.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Date of declaration for distribution of cash, stock, or units to a member or limited partner of limited liability company (LLC) or limited partnership (LP), in CCYY-MM-DD format.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Date of distribution for distribution of cash, stock, or units to a member or limited partner of limited liability company (LLC) or limited partnership (LP), in CCYY-MM-DD format.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Per-share or per-unit cash distributions declared to a common shareholder or unit-holder by an LLC or LP.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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Balance Type:	na
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- Definition

The number of units sold in a public offering of each class of partners' capital account. Units represent shares of ownership of the general, limited, and preferred partners.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 16

-Subparagraph a, b

-Article 6

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 5

-Subparagraph (SAB TOPIC 4.F)

-URI http://asc.fasb.org/extlink&oid=6959260&loc=d3e187171-122770

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Emerging Issues Task Force (EITF)

-Number 87-21

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Practice Bulletin (PB)

-Number 14

-Paragraph 15

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow from the issuance of common limited partners units during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 19

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 18

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 14

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3255-108585

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Equity (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	0 Months Ended										1 Months Ended		3 Months Ended											12 Months Ended
	Nov. 19, 2012	Aug. 17, 2012	May 14, 2012	Mar. 16, 2012	Jan. 13, 2012	Dec. 19, 2011	Oct. 13, 2011	Jul. 13, 2011	Jan. 14, 2011	Apr. 06, 2010	Dec. 31, 2012	Nov. 30, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Distributions of Available Cash
Declaration Date													Oct. 25, 2012	Jul. 26, 2012	Apr. 26, 2012	Jan. 26, 2012	Oct. 18, 2011	Jul. 21, 2011	Apr. 21, 2011	Jan. 27, 2011	Oct. 27, 2010	Jul. 22, 2010	Apr. 22, 2010	Jan. 23, 2013
Record Date													Nov. 07, 2012	Aug. 06, 2012	May 07, 2012	Feb. 06, 2012	Nov. 07, 2011	Aug. 01, 2011	May 02, 2011	Feb. 07, 2011	Nov. 08, 2010	Aug. 02, 2010	May 03, 2010	Feb. 06, 2013
Payment Date													Nov. 14, 2012	Aug. 14, 2012	May 15, 2012	Feb. 14, 2012	Nov. 14, 2011	Aug. 12, 2011	May 13, 2011	Feb. 14, 2011	Nov. 12, 2010	Aug. 13, 2010	May 14, 2010	Feb. 14, 2013
Distribution per common unit (in dollars per unit)													$ 0.81	$ 0.80	$ 0.79	$ 0.76	$ 0.73	$ 0.70	$ 0.67	$ 0.65	$ 0.64	$ 0.64	$ 0.64	$ 0.82
Equity Offerings
Issuance of units in public equity offerings, net of offering costs (in units)	9,800	6,900	8,000	6,800	700	10,000	5,800	4,000	3,500	4,900	100
Net proceeds from public offering after deducting underwriters fees and other third-party expenses	$ 437,000,000	$ 338,000,000	$ 427,000,000	$ 388,000,000	$ 38,000,000	$ 521,000,000	$ 251,000,000	$ 185,000,000	$ 138,000,000	$ 142,000,000	$ 6,000,000													$ 1,634,081,000	$ 1,095,488,000	$ 142,255,000
Maximum amount of limited partner interests that can be sold through the Manager												$ 600,000,000
Maximum
Equity
Period after the end of each quarter within which available cash is distributed to unitholders																								45 days
Period for which cash reserves are created for distribution to unitholders																								1 year