Income Taxes - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 USD ($) Assets	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) Assets	Dec. 31, 2014
Income Taxes [Line Items]
Percentage of distributed taxable income to qualify as a REIT	90.00%
Number of years the Company distributed sufficient taxable income in order to meet REIT distribution requirements	3 years
U.S. federal income taxes	$ 0	$ 0	$ 0
U.S. federal excise taxes	$ 0	0	0
Number of subsequent taxable years	4 years
Tax cost basis of assets	$ 9,100,000,000	9,800,000,000
Net payment	700,000	1,000,000	1,500,000
Tax expense	12,418,000	1,781,000	$ 6,286,000
Withholding tax rate			10.00%
Puerto Rico [Member]
Income Taxes [Line Items]
Number of properties | Assets			14
Prepay of taxes			$ 20,200,000
Prepaid tax asset	$ 4,000,000	$ 16,200,000	16,800,000
Tax expense			$ 3,400,000
Effective tax rate spread			2.00%
Effective tax rate			12.00%
Withholding tax rate			10.00%
Effective tax rate on capital gains			12.00%	29.00%
Number of properties sold | Assets	2
Prepaid tax asset released	$ 1,400,000
Aggregate valuation allowance	$ 10,800,000