Investment in Joint Ventures - Company's Share of Unconsolidated Joint Ventures' Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments	$ 1,829	$ 1,175	$ 3,915	$ 3,095
Sovran HHF Storage Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments	1,320	934	3,103	2,643
Sovran HHF Storage Holdings II LLC [Member]
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments	642	474	1,543	1,364
Other Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments	$ (133)	$ (233)	$ (731)	$ (912)