Debt Instrument, Discount, Percentage

No definition available.

Name:	semg_DebtInstrumentDiscountPercentage
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Period Type:	instant

- Definition

Debt Instrument Redemption Price Percentage of Principal

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument Redemption Price, Prior to Redemption Dates, Premium, Percentage

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument Redemption Price, Upon Change in Control, Percentage

+ References

No definition available.

+ Details

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- Definition

percentage of holders to call debt upon default

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 30
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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Amount, after accumulated amortization, of debt discount.

+ References

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-Name Accounting Standards Codification
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+ Details

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

- Definition

Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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+ Details

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

- Definition

Gross amount of debt extinguished.

+ References

No definition available.

+ Details

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

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

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-Publisher FASB
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+ Details

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

- Definition

Amount of interest capitalized during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Allowance for Funds Used during Construction
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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of the cost of borrowed funds accounted for as interest expense for debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
-Paragraph 2
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+ Details

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

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The effective interest rate at the end of the reporting period.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

Name:	us-gaap_LongTermDebtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

+ References

No definition available.

+ Details

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

- Definition

The excess of the (1) fair value of consideration transferred to the holders of a security in excess of (2) the carrying amount of the security reported on the registrant's balance sheet, which will be deducted from net earnings to derive net earnings available to common shareholders. This amount is generally an adjustment considered in the computation of earnings per share.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Write-off of amounts previously capitalized as debt issuance cost in an extinguishment of debt.

+ References

+ Details

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

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Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=semg_SeniorUnsecuredNotesdue2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=semg_SeniorUnsecuredNotesdue2025Member
Namespace Prefix:
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Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=semg_CorporateCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=semg_SemMexicoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=semg_MXPfacilityMember
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Data Type:	na
Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

- Details

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Period Type:

- Details

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Data Type:	na
Balance Type:
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Long-Term Debt (Details Textual) MXN in Millions			3 Months Ended		6 Months Ended
Long-Term Debt (Details Textual) MXN in Millions	Mar. 17, 2017 USD ($)	Mar. 15, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 MXN	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Loss on early extinguishment of debt			$ 8,000	$ 0	$ 19,930,000	$ 0
Redemption Premium					15,900,000
Write off of Deferred Debt Issuance Cost					3,600,000
Interest Costs Capitalized					12,000,000	3,900,000
Bilateral Letter of Credit [Member]
Debt Instrument [Line Items]
Letters of credit outstanding			$ 50,300,000		$ 50,300,000
Interest rate in effect			1.75%		1.75%		1.75%
Letter of Credit [Member]
Debt Instrument [Line Items]
Letters of credit outstanding			$ 33,800,000		$ 33,800,000
Interest rate in effect			2.25%		2.25%		2.25%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Interest Expense, Debt			$ 3,200,000	1,200,000	$ 5,600,000	2,600,000
Maximum borrowing capacity			1,000,000,000		1,000,000,000
Borrowings outstanding			164,000,000		164,000,000
Senior Unsecured Notes due 2021 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 300,000,000	0		0			$ 300,000,000
Interest Expense, Debt			0	5,800,000	5,000,000	11,700,000
Debt Instrument, Interest Rate, Stated Percentage		7.50%
Senior Unsecured Notes due 2022 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			400,000,000		400,000,000			400,000,000
Interest Expense, Debt			5,900,000	5,900,000	11,800,000	11,700,000
Debt Instrument, Face Amount			$ 400,000,000		$ 400,000,000
Debt Instrument, Interest Rate, Stated Percentage			5.625%		5.625%		5.625%
Senior unsecured notes due 2023 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 350,000,000		$ 350,000,000			350,000,000
Interest Expense, Debt			5,200,000	$ 5,200,000	10,400,000	$ 10,400,000
Debt Instrument, Face Amount			$ 350,000,000		$ 350,000,000
Debt Instrument, Interest Rate, Stated Percentage			5.625%		5.625%		5.625%
Debt Instrument, Unamortized Discount			$ 4,599,000		$ 4,599,000			4,894,000
Senior Unsecured Notes due 2025 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
percentage of holders to call debt upon default					25.00%
Debt Instrument Redemption Price, Prior to Redemption Dates, Premium, Percentage					106.375%
Debt Instrument Redemption Price, Upon Change in Control, Percentage					101.00%
Long-term Debt, Gross			325,000,000		$ 325,000,000			0
Interest Expense, Debt			5,400,000		$ 6,400,000
Debt Instrument, Face Amount	$ 325,000,000
Debt Instrument, Interest Rate, Stated Percentage	6.375%
Debt Instrument Redemption Price Percentage of Principal					35.00%
Debt Instrument, Discount, Percentage	98.467%
Debt Instrument, Unamortized Discount	$ 5,000,000		4,843,000		$ 4,843,000			0
Proceeds from Issuance of Debt	315,500,000
Debt Issuance Costs, Gross	4,500,000
Corporate Credit Facility [Member] \| Revolving Credit Facility [Member] \| Line of Credit [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			164,000,000		164,000,000			$ 20,000,000
SemMexico [Member] \| MXP facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity			3,900,000		3,900,000		MXN 70.0
Borrowings outstanding			0		0
SemMexico [Member] \| Letter of Credit [Member]
Debt Instrument [Line Items]
Letters of credit outstanding			$ 16,200,000		$ 16,200,000		MXN 292.8
Interest rate in effect			0.28%		0.28%		0.28%
Alternate Base Rate [Member] \| Corporate Credit Facility [Member] \| Revolving Credit Facility [Member] \| Line of Credit [Member]
Debt Instrument [Line Items]
Borrowings outstanding			$ 34,000,000		$ 34,000,000
Interest rate in effect			5.50%		5.50%		5.50%
Eurodollar [Member] \| Corporate Credit Facility [Member] \| Revolving Credit Facility [Member] \| Line of Credit [Member]
Debt Instrument [Line Items]
Borrowings outstanding			$ 130,000,000		$ 130,000,000
Interest rate in effect			3.47%		3.47%		3.47%
Mexican bank prime rate [Member] \| SemMexico [Member] \| MXP facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					1.50%
Fair Value, Inputs, Level 2 [Member] \| Senior Unsecured Notes due 2022 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Fair Value			$ 385,000,000		$ 385,000,000
Fair Value, Inputs, Level 2 [Member] \| Senior unsecured notes due 2023 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Fair Value			343,000,000		343,000,000
Fair Value, Inputs, Level 2 [Member] \| Senior Unsecured Notes due 2025 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Fair Value			$ 316,000,000		$ 316,000,000
Tender Offer [Member] \| Senior Unsecured Notes due 2021 [Member]
Debt Instrument [Line Items]
Extinguishment of Debt, Amount		$ 290,000,000
Notes called [Member] \| Senior Unsecured Notes due 2021 [Member]
Debt Instrument [Line Items]
Extinguishment of Debt, Amount	$ 10,000,000