Recent Accounting Pronouncements - Additional Information (Detail)	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($) Property	Jun. 30, 2019 USD ($) Property	Jan. 01, 2019 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of leased real estate properties under extension options, operates for self-storage facilities | Property	2	2
Number of leased properties under purchase options | Property	1	1
Option to purchase property under lease		$ 13,300,000
Operating lease expenses	$ 600,000	$ 1,300,000
Weighted average remaining lease term	10 years 6 months	10 years 6 months
Weighted average discount rate	5.30%	5.30%
Finance Lease, Liability	$ 0	$ 0
Operating lease commitments	19,218,000	19,218,000
ASU 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use assets and related lease liabilities			$ 16,000,000
Operating lease, aggregate right-of-use assets	$ 15,000,000.0	$ 15,000,000.0
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsMember	us-gaap:OtherAssetsMember
Operating lease liabilities	$ 14,400,000	$ 14,400,000
Operating Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:AccountsPayableAndAccruedLiabilitiesMember	us-gaap:AccountsPayableAndAccruedLiabilitiesMember
ASU 2016-02 [Member] | Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Percentage of remaining economic life of asset to define the lease term, major part		75.00%
Percentage of fair value of underlying asset to define the lease term, substantially all		90.00%
ASU 2016-02 [Member] | Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Percentage of total economic life of underlying asset to define the lease term, at or near the end		25.00%
Revenue [Member] | Product Concentration [Member] | Revenue From Rental Products [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Concentration risk, percentage		90.00%