Description of the Business - Additional Information (Detail) shares in Millions	12 Months Ended
	Dec. 31, 2017 Segment shares
Description Of Business And Basis Of Presentation [Line Items]
Number of reportable segments | Segment	2
Percentage of common limited partnership interest	2.59%
Class A Common [Member]
Description Of Business And Basis Of Presentation [Line Items]
Class of common limited partnership units designated as class A common units | shares	8.9
General Partner
Description Of Business And Basis Of Presentation [Line Items]
Percentage of ownership in operating partnership	97.41%
Preferred [Member]
Description Of Business And Basis Of Presentation [Line Items]
Percentage of ownership in operating partnership	100.00%