Selected Quarterly Financial Data (Details) - USD ($)	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
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 33,258,000		$ 31,175,000		$ 28,620,000		$ 42,485,000		$ 35,628,000		$ 35,912,000		$ 35,660,000		$ 36,883,000		$ 135,538,000	$ 144,083,000	$ 152,020,000
Net (loss) income	6,183,000		1,404,000		(6,009,000)		(2,098,000)		(9,914,000)		2,947,000		5,544,000		2,989,000		(520,000)	1,566,000	4,358,000
Net (loss) income attributable to common shareholders	$ 3,316,000		$ (1,421,000)		$ (8,785,000)		$ (4,934,000)		$ (12,657,000)		$ 92,000		$ 2,695,000		$ 194,000		$ (11,824,000)	$ (9,676,000)	$ (10,481,000)
Per common share (basic and diluted)	$ 0.25	[1]	$ (0.11)	[1]	$ (0.67)	[1]	$ (0.39)	[1]	$ (0.98)	[1]	$ 0.00	[1]	$ 0.20	[1]	$ 0.00	[1]	$ (0.92)	$ (0.78)	$ (0.83)

[1] Differences between the sum of the four quarterly per share amounts and the annual per share amounts, if any, are attributable to the effect of the weighted average outstanding share calculation for the respective periods.