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Equity-Based Compensation - Summarizes Information Related to Awards (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restricted stock awards
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Non-vested shares outstanding at December 31, beginning balance	5,136,556
Granted, shares	4,059,225
Vested, shares	(2,656,483)
Forfeited, shares	(803,131)
Non-vested shares outstanding at December 31, ending balance	5,736,167	5,136,556
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Non-vested shares outstanding at December 31, beginning balance, weighted average grant date fair value per share (in dollars per share)	$ 10.81
Granted, weighted average grant date fair value per share (in dollars per share)	6.61	$ 10.20	$ 15.03
Vested, weighted average grant date fair value per share (in dollars per share)	9.52
Forfeited, weighted average grant date fair value per share (in dollars per share)	8.42
Non-vested shares outstanding at December 31, ending balance, weighted average grant date fair value per share (in dollars per share)	$ 8.77	$ 10.81
Performance share unit awards
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Non-vested shares outstanding at December 31, beginning balance	2,032,212
Granted, shares	1,685,090
Vested, shares	(423,953)
Forfeited, shares	(266,125)
Non-vested shares outstanding at December 31, ending balance	3,027,224	2,032,212
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Non-vested shares outstanding at December 31, beginning balance, weighted average grant date fair value per share (in dollars per share)	$ 10.94
Granted, weighted average grant date fair value per share (in dollars per share)	6.80	$ 12.71	16.89
Vested, weighted average grant date fair value per share (in dollars per share)	7.45
Forfeited, weighted average grant date fair value per share (in dollars per share)	10.97
Non-vested shares outstanding at December 31, ending balance, weighted average grant date fair value per share (in dollars per share)	$ 9.12	$ 10.94
Phantom units
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Non-vested shares outstanding at December 31, beginning balance	143,089
Granted, shares	341,290
Vested, shares	(46,334)
Forfeited, shares	(76,043)
Non-vested shares outstanding at December 31, ending balance	362,002	143,089
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Non-vested shares outstanding at December 31, beginning balance, weighted average grant date fair value per share (in dollars per share)	$ 20.85
Vested, weighted average grant date fair value per share (in dollars per share)	20.33
Forfeited, weighted average grant date fair value per share (in dollars per share)	19.30
Non-vested shares outstanding at December 31, ending balance, weighted average grant date fair value per share (in dollars per share)	$ 19.09	$ 20.85
Restricted unit awards | OMP LTIP
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Non-vested shares outstanding at December 31, beginning balance	17,260
Granted, shares	16,170
Vested, shares	(17,260)
Forfeited, shares	0
Non-vested shares outstanding at December 31, ending balance	16,170	17,260
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Non-vested shares outstanding at December 31, beginning balance, weighted average grant date fair value per share (in dollars per share)	$ 17.55
Granted, weighted average grant date fair value per share (in dollars per share)	18.57	$ 17.55	$ 17.00
Vested, weighted average grant date fair value per share (in dollars per share)	17.55
Forfeited, weighted average grant date fair value per share (in dollars per share)	0
Non-vested shares outstanding at December 31, ending balance, weighted average grant date fair value per share (in dollars per share)	$ 18.57	$ 17.55

X

- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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