Debt Instrument, Covenant, Leverage Ratio, EBITDA Metric

No definition available.

Name:	omp_DebtInstrumentCovenantLeverageRatioEBITDAMetric
Namespace Prefix:	omp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Debt Instrument, Covenant, Maximum Consolidated Senior Secured Leverage Ratio

+ References

No definition available.

+ Details

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Namespace Prefix:	omp_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Covenant, Minimum Consolidated Interest Coverage Ratio

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Debt instrument, Covenant, Maximum Consolidated Total Leverage Ratio

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Line of Credit Facility, Maximum Borrowing Capacity, Accordian Feature

+ References

No definition available.

+ Details

Name:	omp_LineofCreditFacilityMaximumBorrowingCapacityAccordianFeature
Namespace Prefix:	omp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

+ References

+ Details

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

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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

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

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

- Details

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- Details

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- Details

Name:	omp_DebtCovenantPeriodAxis=us-gaap_DebtInstrumentRedemptionPeriodThreeMember
Namespace Prefix:
Data Type:	na
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_LongtermDebtTypeAxis=omp_ABRLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
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Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=omp_EurodollarLoansMember
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Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
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Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
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Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=omp_ABRLoansorSwinglineLoansMember
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Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_FederalFundsEffectiveSwapRateMember
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Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_BridgeLoanMember
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Long-Term Debt (Details)	12 Months Ended
Long-Term Debt (Details)	Dec. 31, 2018 USD ($)	Nov. 19, 2018 USD ($)	Aug. 27, 2018 USD ($)	Dec. 31, 2017	Sep. 25, 2017 USD ($)
Line of Credit Facility [Line Items]
Maximum consolidated senior secured leverage ratio	3.75
Covenant Period One
Line of Credit Facility [Line Items]
Maximum consolidated total leverage ratio	4.50
Minimum consolidated interest coverage ratio	3.00
Covenant Period Two
Line of Credit Facility [Line Items]
Maximum consolidated total leverage ratio	5.00
Minimum consolidated interest coverage ratio	2.50
Covenant Period Three
Line of Credit Facility [Line Items]
Maximum consolidated total leverage ratio	5.25
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Borrowing capacity increase limit		$ 600,000,000	$ 400,000,000
Minimum aggregate principal amount threshold under covenant	$ 150,000,000
ABR Loans \| Revolving Credit Facility [Member] \| Adjusted (LIBOR) Rate
Line of Credit Facility [Line Items]
Spread on variable rate (percent)	1.00%
Eurodollar Loans \| Revolving Credit Facility [Member] \| Adjusted (LIBOR) Rate \| Minimum
Line of Credit Facility [Line Items]
Spread on variable rate (percent)	1.75%
Eurodollar Loans \| Revolving Credit Facility [Member] \| Adjusted (LIBOR) Rate \| Maximum
Line of Credit Facility [Line Items]
Spread on variable rate (percent)	2.75%
ABR Loans or Swingline Loans \| Revolving Credit Facility [Member] \| Federal Funds Effective Rate \| Minimum
Line of Credit Facility [Line Items]
Spread on variable rate (percent)	0.75%
ABR Loans or Swingline Loans \| Revolving Credit Facility [Member] \| Federal Funds Effective Rate \| Maximum
Line of Credit Facility [Line Items]
Spread on variable rate (percent)	1.75%
ABR Loans or Swingline Loans \| Revolving Credit Facility [Member] \| Adjusted (LIBOR) Rate \| Minimum
Line of Credit Facility [Line Items]
Spread on variable rate (percent)	0.75%
ABR Loans or Swingline Loans \| Revolving Credit Facility [Member] \| Adjusted (LIBOR) Rate \| Maximum
Line of Credit Facility [Line Items]
Spread on variable rate (percent)	1.75%
The Credit Agreement \| Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Maximum aggregate commitment amount		400,000,000	$ 250,000,000		$ 200,000,000
Amounts outstanding under credit facility	$ 318,000,000
Unused borrowing capacity	$ 82,000,000
Weighted average interest rate (percent)	4.20%			3.20%
The Credit Agreement \| Swingline Loans
Line of Credit Facility [Line Items]
Maximum aggregate commitment amount		$ 10,000,000