Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended			12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2017
Income Taxes [Line Items]
Minimum Distribution Percentage of Taxable Income to Qualify for Real Estate Investment Trust	90.00%
TCJA enacted date	Dec. 22, 2017
U.S. federal corporate tax rate	21.00%			35.00%
TCJA one time transition tax	$ 0
Effect of change in income tax associated with the ACT		$ 4,500,000
Income tax expense	1,935,000		$ 2,485,000
Liabilities for uncertain tax positions	$ 0	$ 0		$ 0