Description of the Business and Basis of Presentation (Detail)			12 Months Ended
Oct. 31, 2012	Mar. 27, 2012	Dec. 31, 2018
Description Of Business And Basis Of Presentation [Line Items]
Date of partnership formation		Mar. 27, 2012
Date for initial public offering completed	Oct. 31, 2012
Number of reportable segments			2

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

No definition available.

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration