Long-Term Debt - Debt Marginal Rates (Details)	12 Months Ended
	Dec. 31, 2018
Less than or equal to 3.00 to 1.00 [Member] | Maximum
Debt Instrument [Line Items]
Consolidated total leverage ratio	3.00
Greater than 3.00 to 1.00 but less than or equal to 3.50 to 1.00 [Member] | Minimum
Debt Instrument [Line Items]
Consolidated total leverage ratio	3.00
Greater than 3.00 to 1.00 but less than or equal to 3.50 to 1.00 [Member] | Maximum
Debt Instrument [Line Items]
Consolidated total leverage ratio	3.50
Greater than 3.50 to 1.00 but less than or equal to 4.00 to 1.00 [Member] | Minimum
Debt Instrument [Line Items]
Consolidated total leverage ratio	3.50
Greater than 3.50 to 1.00 but less than or equal to 4.00 to 1.00 [Member] | Maximum
Debt Instrument [Line Items]
Consolidated total leverage ratio	4.00
Greater than 4.00 to 1.00 but less than or equal to 4.50 to 1.00 [Member] | Minimum
Debt Instrument [Line Items]
Consolidated total leverage ratio	4.00
Greater than 4.00 to 1.00 but less than or equal to 4.50 to 1.00 [Member] | Maximum
Debt Instrument [Line Items]
Consolidated total leverage ratio	4.50
Greater than 4.50 to 1.00 [Member] | Minimum
Debt Instrument [Line Items]
Consolidated total leverage ratio	4.50
OMP Revolving Line of Credit [Member] | Less than or equal to 3.00 to 1.00 [Member]
Debt Instrument [Line Items]
Commitment fee rate (percent)	0.375%
OMP Revolving Line of Credit [Member] | Less than or equal to 3.00 to 1.00 [Member] | Eurodollar Loans [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	1.75%
OMP Revolving Line of Credit [Member] | Less than or equal to 3.00 to 1.00 [Member] | Alternate Based Rate (ABR) [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	0.75%
OMP Revolving Line of Credit [Member] | Greater than 3.00 to 1.00 but less than or equal to 3.50 to 1.00 [Member]
Debt Instrument [Line Items]
Commitment fee rate (percent)	0.375%
OMP Revolving Line of Credit [Member] | Greater than 3.00 to 1.00 but less than or equal to 3.50 to 1.00 [Member] | Eurodollar Loans [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	2.00%
OMP Revolving Line of Credit [Member] | Greater than 3.00 to 1.00 but less than or equal to 3.50 to 1.00 [Member] | Alternate Based Rate (ABR) [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	1.00%
OMP Revolving Line of Credit [Member] | Greater than 3.50 to 1.00 but less than or equal to 4.00 to 1.00 [Member]
Debt Instrument [Line Items]
Commitment fee rate (percent)	0.50%
OMP Revolving Line of Credit [Member] | Greater than 3.50 to 1.00 but less than or equal to 4.00 to 1.00 [Member] | Eurodollar Loans [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	2.25%
OMP Revolving Line of Credit [Member] | Greater than 3.50 to 1.00 but less than or equal to 4.00 to 1.00 [Member] | Alternate Based Rate (ABR) [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	1.25%
OMP Revolving Line of Credit [Member] | Greater than 4.00 to 1.00 but less than or equal to 4.50 to 1.00 [Member]
Debt Instrument [Line Items]
Commitment fee rate (percent)	0.50%
OMP Revolving Line of Credit [Member] | Greater than 4.00 to 1.00 but less than or equal to 4.50 to 1.00 [Member] | Eurodollar Loans [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	2.50%
OMP Revolving Line of Credit [Member] | Greater than 4.00 to 1.00 but less than or equal to 4.50 to 1.00 [Member] | Alternate Based Rate (ABR) [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	1.50%
OMP Revolving Line of Credit [Member] | Greater than 4.50 to 1.00 [Member]
Debt Instrument [Line Items]
Commitment fee rate (percent)	0.50%
OMP Revolving Line of Credit [Member] | Greater than 4.50 to 1.00 [Member] | Eurodollar Loans [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	2.75%
OMP Revolving Line of Credit [Member] | Greater than 4.50 to 1.00 [Member] | Alternate Based Rate (ABR) [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	1.75%