Investment in Storage Facilities - Schedule of Acquired Facilities and Purchase Price of Facilities (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 Facility	Mar. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Number of Properties	7
Purchase Price	$ 95,350
Cash Paid	94,601
Loan Assumed
Net Other Liabilities (Assets) Assumed	749
Land	34,019
Acquisition Date Building, Equipment, and Improvements	59,835
Fair Value In-Place Customers Leases	1,496
Closing Costs Expensed	2,778	486
Florida [Member] | Date Of Acquisition, 1/9/2014 [Member]
Finite-Lived Intangible Assets [Line Items]
Number of Properties	2
Date of Acquisition	Jan. 09, 2014
Purchase Price	54,000
Cash Paid	53,599
Loan Assumed
Net Other Liabilities (Assets) Assumed	401
Land	23,309
Acquisition Date Building, Equipment, and Improvements	29,867
Fair Value In-Place Customers Leases	824
Closing Costs Expensed	1,691
Texas [Member] | Date Of Acquisition, 1/17/2014 [Member]
Finite-Lived Intangible Assets [Line Items]
Number of Properties	1
Date of Acquisition	Jan. 17, 2014
Purchase Price	9,000
Cash Paid	8,962
Loan Assumed
Net Other Liabilities (Assets) Assumed	38
Land	3,999
Acquisition Date Building, Equipment, and Improvements	4,856
Fair Value In-Place Customers Leases	145
Closing Costs Expensed	225
Texas [Member] | Date Of Acquisition, 2/10/2014 [Member]
Finite-Lived Intangible Assets [Line Items]
Number of Properties	1
Date of Acquisition	Feb. 10, 2014
Purchase Price	8,900
Cash Paid	8,857
Loan Assumed
Net Other Liabilities (Assets) Assumed	43
Land	2,235
Acquisition Date Building, Equipment, and Improvements	6,564
Fair Value In-Place Customers Leases	101
Closing Costs Expensed	212
Maine [Member] | Date Of Acquisition, 2/11/2014 [Member]
Finite-Lived Intangible Assets [Line Items]
Number of Properties	2
Date of Acquisition	Feb. 11, 2014
Purchase Price	14,750
Cash Paid	14,601
Loan Assumed
Net Other Liabilities (Assets) Assumed	149
Land	2,639
Acquisition Date Building, Equipment, and Improvements	11,824
Fair Value In-Place Customers Leases	287
Closing Costs Expensed	426
Illinois [Member] | Date Of Acquisition, 3/31/2014 [Member]
Finite-Lived Intangible Assets [Line Items]
Number of Properties	1
Date of Acquisition	Mar. 31, 2014
Purchase Price	8,700
Cash Paid	8,582
Loan Assumed
Net Other Liabilities (Assets) Assumed	118
Land	1,837
Acquisition Date Building, Equipment, and Improvements	6,724
Fair Value In-Place Customers Leases	139
Closing Costs Expensed	$ 224