Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Convertible Stock	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Balance, beginning of period at Dec. 31, 2018	$ 263,466	$ 1	$ 612	$ 539,493	$ (379)	$ (276,261)
Balance, beginning of period (in shares) at Dec. 31, 2018		50,000	61,379,000
Common stock issued through distribution reinvestment plan	4,864		$ 6	4,858
Common stock issued through distribution reinvestment plan (in shares)			570,000
Distributions declared	(6,132)					(6,132)
Common stock redemptions	(5,953)		$ (7)	(5,946)
Common stock redemptions (in shares)			(664,000)
Designated derivatives, fair value adjustment	32				32
Net income (loss)	11,697					11,697
Balance, end of period at Mar. 31, 2019	267,974	$ 1	$ 611	538,405	(347)	(270,696)
Balance, end of period (in shares) at Mar. 31, 2019		50,000	61,285,000
Balance, beginning of period at Dec. 31, 2018	263,466	$ 1	$ 612	539,493	(379)	(276,261)
Balance, beginning of period (in shares) at Dec. 31, 2018		50,000	61,379,000
Designated derivatives, fair value adjustment	130
Net income (loss)	(5,100)
Balance, end of period at Sep. 30, 2019	227,779	$ 1	$ 598	527,146	(249)	(299,717)
Balance, end of period (in shares) at Sep. 30, 2019		50,000	59,936,000
Balance, beginning of period at Dec. 31, 2018	263,466	$ 1	$ 612	539,493	(379)	(276,261)
Balance, beginning of period (in shares) at Dec. 31, 2018		50,000	61,379,000
Balance, end of period at Dec. 31, 2019	$ 216,313	$ 1	$ 600	528,464	(189)	(312,563)
Balance, end of period (in shares) at Dec. 31, 2019	60,094,623	50,000	60,095,000
Balance, beginning of period at Mar. 31, 2019	$ 267,974	$ 1	$ 611	538,405	(347)	(270,696)
Balance, beginning of period (in shares) at Mar. 31, 2019		50,000	61,285,000
Common stock issued through distribution reinvestment plan	3,308		$ 4	3,304
Common stock issued through distribution reinvestment plan (in shares)			397,000
Distributions declared	(6,045)					(6,045)
Common stock redemptions	(13,946)		$ (16)	(13,930)
Common stock redemptions (in shares)			(1,671,000)
Designated derivatives, fair value adjustment	50				50
Net income (loss)	(8,109)					(8,109)
Balance, end of period at Jun. 30, 2019	243,232	$ 1	$ 599	527,779	(297)	(284,850)
Balance, end of period (in shares) at Jun. 30, 2019		50,000	60,011,000
Common stock issued through distribution reinvestment plan	3,269		$ 4	3,265
Common stock issued through distribution reinvestment plan (in shares)			392,000
Distributions declared	(6,179)					(6,179)
Common stock redemptions	(3,903)		$ (5)	(3,898)
Common stock redemptions (in shares)			(467,000)
Designated derivatives, fair value adjustment	48				48
Net income (loss)	(8,688)					(8,688)
Balance, end of period at Sep. 30, 2019	227,779	$ 1	$ 598	527,146	(249)	(299,717)
Balance, end of period (in shares) at Sep. 30, 2019		50,000	59,936,000
Balance, beginning of period at Dec. 31, 2019	$ 216,313	$ 1	$ 600	528,464	(189)	(312,563)
Balance, beginning of period (in shares) at Dec. 31, 2019	60,094,623	50,000	60,095,000
Common stock issued through distribution reinvestment plan	$ 3,131		$ 4	3,127
Common stock issued through distribution reinvestment plan (in shares)			371,000
True-up of prior year cash distributions declared	(11)					(11)
Common stock redemptions	(1,225)		$ (2)	(1,223)
Common stock redemptions (in shares)			(140,000)
Designated derivatives, fair value adjustment	73				73
Net income (loss)	(7,926)					(7,926)
Balance, end of period at Mar. 31, 2020	210,355	$ 1	$ 602	530,368	(116)	(320,500)
Balance, end of period (in shares) at Mar. 31, 2020		50,000	60,326,000
Balance, beginning of period at Dec. 31, 2019	$ 216,313	$ 1	$ 600	528,464	(189)	(312,563)
Balance, beginning of period (in shares) at Dec. 31, 2019	60,094,623	50,000	60,095,000
Common stock issued through distribution reinvestment plan	$ 3,131
True-up of prior year cash distributions declared	(11)
Designated derivatives, fair value adjustment	(36)
Net income (loss)	(24,158)
Balance, end of period at Sep. 30, 2020	$ 192,926	$ 1	$ 601	529,281	(225)	(336,732)
Balance, end of period (in shares) at Sep. 30, 2020	60,206,977	50,000	60,207,000
Balance, beginning of period at Mar. 31, 2020	$ 210,355	$ 1	$ 602	530,368	(116)	(320,500)
Balance, beginning of period (in shares) at Mar. 31, 2020		50,000	60,326,000
Common stock redemptions	(1,088)		$ (1)	(1,087)
Common stock redemptions (in shares)			(120,000)
Designated derivatives, fair value adjustment	2				2
Net income (loss)	(6,863)					(6,863)
Balance, end of period at Jun. 30, 2020	202,406	$ 1	$ 601	529,281	(114)	(327,363)
Balance, end of period (in shares) at Jun. 30, 2020		50,000	60,206,000
Common stock redemptions (in shares)			1,000
Designated derivatives, fair value adjustment	(111)				(111)
Net income (loss)	(9,369)					(9,369)
Balance, end of period at Sep. 30, 2020	$ 192,926	$ 1	$ 601	$ 529,281	$ (225)	$ (336,732)
Balance, end of period (in shares) at Sep. 30, 2020	60,206,977	50,000	60,207,000