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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Significant Accounting Policies [Line Items]
Federal Deposit Insurance Corporation deposit insurance limit per institution	$ 250,000
Restricted cash	6,729,000	$ 4,634,000
Bad debt expense	644,000	870,000	$ 975,000
Amortization expense for intangible assets	3,429,000	1,536,000	3,735,000
Write-off of amortized intangible assets	4,153,000	0	0
Amortization expense for intangible assets expected for 2019	744,000
Depreciation expense	41,792,000	32,665,000	31,089,000
Write-off of fully depreciated fixed assets	408,000
Recognized contract assets	0
Recognized contract liabilities	0
Advertising expenses	2,172,000	1,806,000	1,749,000
Income tax expense	$ 0	$ 0	$ 0
Taxable income distributable to stockholders	90.00%
Dividends characterized as capital gain distribution	37.00%	53.00%
Dividends characterized as ordinary income percentage	39.00%	36.00%
Dividends characterized as return of capital	24.00%	11.00%	7.00%
Dividends characterized as ordinary taxable income			93.00%
ASC Topic 230
Significant Accounting Policies [Line Items]
Increase (decrease) in net cash used in investing activities due to new accounting standard adoption		$ 942,000	$ (105,000)
Natural Disasters and Other Insurable Events
Significant Accounting Policies [Line Items]
Rent revenue recognized	$ 195,000	110,000
North Carolina
Significant Accounting Policies [Line Items]
Percentage of rental revenue	14.93%
Tennessee
Significant Accounting Policies [Line Items]
Percentage of rental revenue	11.21%
Georgia
Significant Accounting Policies [Line Items]
Percentage of rental revenue	10.95%
Kentucky
Significant Accounting Policies [Line Items]
Percentage of rental revenue	9.76%
South Carolina
Significant Accounting Policies [Line Items]
Percentage of rental revenue	8.73%
Ohio
Significant Accounting Policies [Line Items]
Percentage of rental revenue	8.20%
Texas
Significant Accounting Policies [Line Items]
Percentage of rental revenue	7.87%
Building and Building Improvements
Significant Accounting Policies [Line Items]
Depreciable Lives	40 years
Leases Acquired In Place
Significant Accounting Policies [Line Items]
Acquisition of above-market in-place leases	$ 3,074,000	$ 2,515,000
Minimum \| Equipment and Fixtures
Significant Accounting Policies [Line Items]
Depreciable Lives	5 years
Maximum
Significant Accounting Policies [Line Items]
Cash and cash equivalents original maturity period	3 months
Maximum \| Equipment and Fixtures
Significant Accounting Policies [Line Items]
Depreciable Lives	10 years