Condensed Consolidated Statements of Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	February 2018 Offering [Member] Common Stock [Member]	February 2018 Offering [Member] Additional Paid-in Capital [Member]	February 2018 Offering [Member]	November 2017 ATM Facility [Member] Common Stock [Member]	November 2017 ATM Facility [Member] Additional Paid-in Capital [Member]	November 2017 ATM Facility [Member] Retained Earnings [Member]	November 2017 ATM Facility [Member]	Consultant [Member] Common Stock [Member]	Consultant [Member] Additional Paid-in Capital [Member]	Consultant [Member] Retained Earnings [Member]	Consultant [Member]	Director [Member] Common Stock [Member]	Director [Member] Additional Paid-in Capital [Member]	Director [Member] Retained Earnings [Member]	Director [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Total
Balances (in shares) at Dec. 31, 2017																19,503,558
Balances at Dec. 31, 2017																$ 2	$ 102,979	$ (105,581)	$ (2,600)
Stock-based compensation expense																	645		645
Issuance of common shares from employee stock purchase plan (in shares)																20,744
Issuance of common shares from employee stock purchase plan																	65		65
Issuance of restricted shares (in shares)																22,137
Issuance of restricted shares																	108		108
Net loss																		(12,669)	(12,669)
Stock offering, net of issuance costs (in shares)	11,500,000			208,277
Stock offering, net of issuance costs	$ 1	$ 32,224	$ 32,225		$ 1,011		$ 1,011
Cumulative effect adjustment from adoption of new accounting standard – ASC 606																		177	177
Balances (in shares) at Mar. 31, 2018																31,254,716
Balances at Mar. 31, 2018																$ 3	137,032	(118,073)	18,962
Balances (in shares) at Dec. 31, 2017																19,503,558
Balances at Dec. 31, 2017																$ 2	102,979	(105,581)	(2,600)
Net loss																			(24,185)
Stock offering, net of issuance costs (in shares)							273,529
Balances (in shares) at Jun. 30, 2018																31,466,508
Balances at Jun. 30, 2018																$ 3	138,283	(129,589)	8,697
Balances (in shares) at Mar. 31, 2018																31,254,716
Balances at Mar. 31, 2018																$ 3	137,032	(118,073)	18,962
Stock-based compensation expense																	709		709
Issuance of common shares from employee stock purchase plan (in shares)																25,618
Issuance of common shares from employee stock purchase plan																	59		59
Issuance of restricted shares (in shares)																20,922
Issuance of restricted shares																	67		67
Issuance of common shares in connection with restricted stock award to employee (in shares)																100,000
Issuance of common shares in connection with restricted stock award to employee																	256		256
Net loss																		(11,516)	(11,516)
Stock offering, net of issuance costs (in shares)				65,252			65,252
Stock offering, net of issuance costs					$ 171		$ 171
February 2018 Offering issuance costs																	(11)		(11)
Balances (in shares) at Jun. 30, 2018																31,466,508
Balances at Jun. 30, 2018																$ 3	138,283	(129,589)	8,697
Balances (in shares) at Dec. 31, 2018																46,363,945
Balances at Dec. 31, 2018																$ 5	160,292	(155,385)	4,912	[1]
Stock-based compensation expense																	470		470
Issuance of common shares from employee stock purchase plan (in shares)																43,759
Issuance of common shares from employee stock purchase plan																	35		35
Issuance of restricted shares (in shares)								27,473
Issuance of restricted shares									$ 25		$ 25
Issuance of common shares in connection with restricted stock award to employee (in shares)																625
Issuance of common shares in connection with restricted stock award to employee																	1		1
Net loss																		(10,029)	(10,029)
Balances (in shares) at Mar. 31, 2019																46,435,802
Balances at Mar. 31, 2019																$ 5	160,823	(165,414)	(4,586)
Balances (in shares) at Dec. 31, 2018																46,363,945
Balances at Dec. 31, 2018																$ 5	160,292	(155,385)	4,912	[1]
Net loss																			(19,753)
Stock offering, net of issuance costs (in shares)							0
Balances (in shares) at Jun. 30, 2019																46,574,958
Balances at Jun. 30, 2019																$ 5	161,464	(175,138)	(13,669)
Balances (in shares) at Mar. 31, 2019																46,435,802
Balances at Mar. 31, 2019																$ 5	160,823	(165,414)	(4,586)
Stock-based compensation expense																	562		562
Issuance of common shares from employee stock purchase plan (in shares)																60,740
Issuance of common shares from employee stock purchase plan																	20		20
Issuance of restricted shares (in shares)								25,000				52,791
Issuance of restricted shares									$ 11		$ 11		$ 48		$ 48
Issuance of common shares in connection with restricted stock award to employee (in shares)																625
Issuance of common shares in connection with restricted stock award to employee
Net loss																		(9,724)	(9,724)
Stock offering, net of issuance costs (in shares)							0
Balances (in shares) at Jun. 30, 2019																46,574,958
Balances at Jun. 30, 2019																$ 5	$ 161,464	$ (175,138)	$ (13,669)

[1] The condensed consolidated balance sheet as of December 31, 2018 has been derived from the audited consolidated financial statements as of that date.