SIGNIFICANT ACCOUNTING POLICIES - Basis of Presentation (Details) - USD ($)					12 Months Ended
	Jul. 15, 2020	Jun. 22, 2020	Dec. 13, 2019	Dec. 11, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Aug. 04, 2020	Aug. 03, 2020	Dec. 31, 2017
Class of Stock [Line Items]
Accumulated deficit					$ 161,766,000	$ 128,822,000
Payments on mortgage notes					125,000	118,000	$ 113,000
Mortgage balance					1,175,000	26,191,000
Follow-on Offering
Class of Stock [Line Items]
Public offering price (in dollars per share)		$ 47.00
Aggregate gross proceeds		$ 75,200,000
Net proceeds on sale of stock		70,207,000
Discounts and commissions		4,512,000
Offering costs		$ 481,000
Common stock issued and sold (in shares)		1,600,000
Common Stock | Second Public Offering
Class of Stock [Line Items]
Issued and sold shares			1,755,000	1,725,000
Public offering price (in dollars per share)			$ 36.50	$ 27.00
Aggregate gross proceeds			$ 64,076,000	$ 46,575,000
Net proceeds on sale of stock			59,996,000	43,423,000
Discounts and commissions			3,845,000	2,800,000
Offering costs			$ 235,000	$ 352,000
Note payable to Squadron
Class of Stock [Line Items]
Mortgage balance					0	19,891,000				$ 20,000,000
Revolving credit facility with Squadron | Revolving Credit Facility
Class of Stock [Line Items]
Mortgage balance					$ 0	$ 5,000,000
Term Note A | Note payable to Squadron
Class of Stock [Line Items]
Payments on mortgage notes	$ 20,000,000
First Amended Loan Agreement | Squadron
Class of Stock [Line Items]
Term loan credit facility								$ 25,000,000	$ 15,000,000