Principal Activity and Significant Accounting Policies - Other (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
PRINCIPAL ACTIVITY AND SIGNIFICANT ACCOUNTING POLICIES
Impairment of lease intangible assets	$ 0	$ 0	$ 0
Taxable income to be distributed	90.00%
Retainable taxable income	10.00%
Tax status
Ordinary income	$ 0.8791	$ 0.7258	$ 0.8124
Capital Gain	0.0048		0.0015
Return of capital	0.1611	0.2917	0.1761
Total	$ 1.0450	$ 1.0175	$ 0.9900
Ordinary income (as a percent)	84.12%	71.33%	82.05%
Capital Gain (as a percent)	0.46%		0.16%
Return of capital (as a percent)	15.42%	28.67%	17.79%
Total (as a percent)	100.00%	100.00%	100.00%
Provisions or liabilities for income taxes	$ 0