Federal Income Tax Reporting - Reconciliation Between GAAP Net Income and Taxable Income, Tax Components of Distributions (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation Between GAAP Net Income and Taxable Income
Net income per GAAP	$ 37,440	$ (1,679)	$ (2,075)	$ (1,071)	$ 3,648	$ 2,399	$ 1,633	$ (1,205)	$ 32,615	$ 6,475	$ 13,069
Adjustments to GAAP net income (loss):
GAAP depreciation and amortization									88,244	90,507	93,675
Tax depreciation and amortization									(79,542)	(66,376)	(62,657)
Tax basis more than GAAP basis on assets sold									(11,450)
Straight line rent adjustment, net									(1,685)	(10,462)	(1,350)
Deferred rent, net									1,956	535	210
Non-taxable distributions											(710)
Other, net									390	4,099	(6,651)
Taxable income									30,528	24,778	35,586
Less: Capital gains recognized									7,576
Taxable income subject to distribution requirement									$ 22,952	$ 24,778	$ 35,586
Tax components of the Company's common distributions paid per share
Ordinary income (in dollars per share)									$ 0.28	$ 0.25	$ 0.35
Capital gain (in dollars per share)									0.06
Return of capital (in dollars per share)									0.02	0.11	0.11
Total (in dollars per share)									$ 0.36	$ 0.36	$ 0.46
Ordinary income (as a percent)									77.51%	69.96%	76.39%
Capital gain (as a percent)									16.72%
Return of capital (as a percent)									5.77%	30.04%	23.61%
Total (as a percent)									100.00%	100.00%	100.00%
Common Stock Dividends Per Share Cash Paid Qualified Distribution										$ 0.009
Qualified distribution as a percentage of total distribution										2.52%