Store Acquisitions - Schedule of Operating Properties Acquired (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2016 USD ($) property store shares	Jun. 30, 2015 USD ($)
Property Acquisitions [Line Items]
Number of Stores | property	45
Total Consideration Paid	$ 469,894
Cash Paid	401,938
Loan Assumed	9,723
Net Liabilities/(Assets) Assumed	(1,996)
Value of OP Units Issued	$ 56,237	$ 106,522
Number of OP Units Issued (in units) | shares	2,215,231
Fair Value Real estate assets	$ 514,078
Massachusetts Property Acquired 6/30/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	1
Total Consideration Paid	$ 13,807
Cash Paid	13,751
Loan Assumed	0
Net Liabilities/(Assets) Assumed	(56)
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 13,807
Georgia Property Acquired 6/30/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	1
Total Consideration Paid	$ 7,993
Cash Paid	6,789
Loan Assumed	0
Net Liabilities/(Assets) Assumed	(4)
Value of OP Units Issued	$ 1,200
Number of OP Units Issued (in units) | shares	13,764
Fair Value Real estate assets	$ 7,993
Illinois Property Acquired 6/10/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | store	4
Total Consideration Paid	$ 55,851
Cash Paid	0
Loan Assumed	0
Net Liabilities/(Assets) Assumed	(814)
Value of OP Units Issued	$ 55,037
Number of OP Units Issued (in units) | shares	2,201,467
Fair Value Real estate assets	$ 55,851
Texas Property Acquired 6/2/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	4
Total Consideration Paid	$ 37,478
Cash Paid	37,246
Loan Assumed	0
Net Liabilities/(Assets) Assumed	(232)
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 37,478
South Carolina Property Acquired 5/10/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	1
Total Consideration Paid	$ 8,249
Cash Paid	8,230
Loan Assumed	0
Net Liabilities/(Assets) Assumed	(19)
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 8,249
Washington, DC Property Acquired 5/5/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	1
Total Consideration Paid	$ 32,968
Cash Paid	23,163
Loan Assumed	9,723
Net Liabilities/(Assets) Assumed	(82)
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 32,968
Indiana Property Acquired 4/22/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	5
Total Consideration Paid	$ 26,983
Cash Paid	26,849
Loan Assumed	0
Net Liabilities/(Assets) Assumed	(134)
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 26,983
Colorado Property Acquired 4/19/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	1
Total Consideration Paid	$ 7,904
Cash Paid	7,869
Loan Assumed	0
Net Liabilities/(Assets) Assumed	(35)
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 7,904
Arizona Property Acquired 4/18/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	1
Total Consideration Paid	$ 8,154
Cash Paid	8,029
Loan Assumed	0
Net Liabilities/(Assets) Assumed	(125)
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 8,154
Texas Property Acquired 4/15/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	1
Total Consideration Paid	$ 10,978
Cash Paid	10,922
Loan Assumed	0
Net Liabilities/(Assets) Assumed	(56)
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 10,978
Arizona Property Acquired 4/5/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	1
Total Consideration Paid	$ 5,000
Cash Paid	4,999
Loan Assumed	0
Net Liabilities/(Assets) Assumed	(1)
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 5,000
Hawaii Property Acquired 4/5/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	1
Total Consideration Paid	$ 28,992
Cash Paid	28,935
Loan Assumed	0
Net Liabilities/(Assets) Assumed	(57)
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 28,992
New Mexico 1 Property Acquired 3/29/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	1
Total Consideration Paid	$ 10,958
Cash Paid	10,928
Loan Assumed	0
Net Liabilities/(Assets) Assumed	(30)
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 10,958
New Mexico 2 Property Acquired 3/29/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	1
Total Consideration Paid	$ 17,940
Cash Paid	17,905
Loan Assumed	0
Net Liabilities/(Assets) Assumed	35
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 17,940
Georgia Property Acquired 3/29/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	3
Total Consideration Paid	$ 25,087
Cash Paid	25,069
Loan Assumed	0
Net Liabilities/(Assets) Assumed	(18)
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 25,087
Texas Property Acquired 3/21/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	1
Total Consideration Paid	$ 9,994
Cash Paid	9,969
Loan Assumed	0
Net Liabilities/(Assets) Assumed	(25)
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 9,994
Illinois Property Acquired 2/25/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	1
Total Consideration Paid	$ 16,721
Cash Paid	16,738
Loan Assumed	0
Net Liabilities/(Assets) Assumed	17
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 16,721
Massachusetts Property Acquired 2/16/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	1
Total Consideration Paid	$ 16,169
Cash Paid	16,174
Loan Assumed	0
Net Liabilities/(Assets) Assumed	5
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 16,169
Florida Maryland Nevada New York Tennessee Property Acquired 2/2/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	6
Total Consideration Paid	$ 53,898
Cash Paid	53,940
Loan Assumed	0
Net Liabilities/(Assets) Assumed	42
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 98,082
Texas Property Acquired 1/14/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	3
Total Consideration Paid	$ 22,625
Cash Paid	22,523
Loan Assumed	0
Net Liabilities/(Assets) Assumed	(102)
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 22,625
Florida Property Acquired 1/12/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	1
Total Consideration Paid	$ 9,001
Cash Paid	8,980
Loan Assumed	0
Net Liabilities/(Assets) Assumed	21
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 9,001
Texas Property Acquired 1/7/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	3
Total Consideration Paid	$ 27,537
Cash Paid	27,435
Loan Assumed	0
Net Liabilities/(Assets) Assumed	102
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 27,537
New Mexico Property Acquired 1/7/2016 [Member]
Property Acquisitions [Line Items]
Number of Stores | property	2
Total Consideration Paid	$ 15,607
Cash Paid	15,495
Loan Assumed	0
Net Liabilities/(Assets) Assumed	112
Value of OP Units Issued	$ 0
Number of OP Units Issued (in units) | shares	0
Fair Value Real estate assets	$ 15,607