Related Party Transactions (Details Textual) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Glass Mountain Pipeline LLC [Member]
Related Party Transactions (Textual) [Abstract]
Related Party Transaction, Expenses from Transactions with Related Party	$ 1,400,000	$ 700,000	$ 3,300,000	$ 1,200,000
Related Party Transaction Reimbursements from Transactions With Related Party	200,000	200,000	400,000	400,000
Related Party Transaction, Purchases from Related Party	0	0	400,000	1,500,000
White Cliffs Pipeline, L.L.C. [Member]
Related Party Transactions (Textual) [Abstract]
Revenues	1,100,000	1,100,000	2,200,000	2,100,000
Related Party Transaction, Expenses from Transactions with Related Party	2,700,000	1,100,000	5,200,000	1,800,000
Related Party Transaction Reimbursements from Transactions With Related Party	100,000	100,000	200,000	200,000
Related Party Transaction, Purchases from Related Party	3,500,000	0	3,500,000	0
Law Firm [Member]
Related Party Transactions (Textual) [Abstract]
Legal fees	300,000	400,000	400,000	700,000
White Cliffs Pipeline, L.L.C. [Member] \| Law Firm [Member]
Related Party Transactions (Textual) [Abstract]
Legal fees	$ 100	$ 100	$ 1,600	$ 3,400

Related party transaction reimbursements from transactions with related party.

No definition available.

Name:	semg_RelatedPartyTransactionReimbursementsFromTransactionsWithRelatedParty
Namespace Prefix:	semg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Related party transactions.

+ References

No definition available.

+ Details

Name:	semg_RelatedPartyTransactionsTextualAbstract
Namespace Prefix:	semg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of expense provided in the period for legal costs incurred on or before the balance sheet date pertaining to resolved, pending or threatened litigation, including arbitration and mediation proceedings.

+ References

+ Details

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

- Definition

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

+ Details

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

- Definition

Purchases during the period (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

No definition available.

+ Details

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

- Definition

Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(e))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Related Parties
-URI http://asc.fasb.org/extlink&oid=16382449

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07.1(c))
-URI http://asc.fasb.org/extlink&oid=6488393&loc=d3e606610-122999

+ Details

Name:	us-gaap_RevenueFromRelatedParties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=semg_GlassMountainPipelineLlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=semg_WhiteCliffsPipelineLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=semg_LawFirmMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=semg_WhiteCliffsPipelineLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: