CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total		Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]
Balances at beginning of period at Dec. 31, 2018	$ 29,371		$ 6	$ 295,116	$ (264,713)	$ (1,038)
Balances at beginning of period (in shares) at Dec. 31, 2018			5,938
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock through equity distribution agreement, net of offering costs	$ 1,504		$ 1	1,503	0	0
Issuance of common stock through equity distribution agreement, net of offering costs (in shares)	570		570
Issuance of common stock from vesting of restricted stock units	$ 0		$ 0	0	0	0
Issuance of common stock from vesting of restricted stock units (in shares)			73
Tax withholding related to vesting of restricted stock units	(251)		$ 0	(251)	0	0
Issuance of common stock under employee stock purchase plan	88		$ 0	88	0	0
Issuance of common stock under employee stock purchase plan (in shares)			42
Stock-based compensation expense	1,447		$ 0	1,447	0	0
Net loss	(8,609)		0	0	(8,609)	0
Foreign currency translation adjustments	5		0	0	0	5
Balances at end of period at Jun. 30, 2019	23,555		$ 7	297,903	(273,322)	(1,033)
Balances at end of period (in shares) at Jun. 30, 2019			6,623
Balances at beginning of period at Dec. 31, 2018	29,371		$ 6	295,116	(264,713)	(1,038)
Balances at beginning of period (in shares) at Dec. 31, 2018			5,938
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(12,408)
Balances at end of period at Dec. 31, 2019	21,060	[1]	$ 7	299,263	(277,112)	(1,098)
Balances at end of period (in shares) at Dec. 31, 2019			6,810
Balances at beginning of period at Mar. 31, 2019	25,323		$ 6	295,745	(269,319)	(1,109)
Balances at beginning of period (in shares) at Mar. 31, 2019			5,954
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock through equity distribution agreement, net of offering costs	$ 1,504		$ 1	1,503	0	0
Issuance of common stock through equity distribution agreement, net of offering costs (in shares)	570		570
Issuance of common stock from vesting of restricted stock units	$ 0		$ 0	0	0	0
Issuance of common stock from vesting of restricted stock units (in shares)			57
Tax withholding related to vesting of restricted stock units	(195)		$ 0	(195)	0	0
Issuance of common stock under employee stock purchase plan	88		$ 0	88	0	0
Issuance of common stock under employee stock purchase plan (in shares)			42
Stock-based compensation expense	762		$ 0	762	0	0
Net loss	(4,003)		0	0	(4,003)	0
Foreign currency translation adjustments	76		0	0	0	76
Balances at end of period at Jun. 30, 2019	23,555		$ 7	297,903	(273,322)	(1,033)
Balances at end of period (in shares) at Jun. 30, 2019			6,623
Balances at beginning of period at Dec. 31, 2019	$ 21,060	[1]	$ 7	299,263	(277,112)	(1,098)
Balances at beginning of period (in shares) at Dec. 31, 2019			6,810
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock through equity distribution agreement, net of offering costs (in shares)	0
Issuance of common stock from vesting of restricted stock units	$ 0		$ 0	0	0	0
Issuance of common stock from vesting of restricted stock units (in shares)			138
Tax withholding related to vesting of restricted stock units	(151)		$ 0	(151)	0	0
Issuance of common stock under employee stock purchase plan	14		$ 0	14	0	0
Issuance of common stock under employee stock purchase plan (in shares)			11
Stock-based compensation expense	1,013		$ 0	1,013	0	0
Net loss	(7,452)		0	0	(7,452)	0
Foreign currency translation adjustments	88		0	0	0	88
Balances at end of period at Jun. 30, 2020	14,572		$ 7	300,139	(284,564)	(1,010)
Balances at end of period (in shares) at Jun. 30, 2020			6,959
Balances at beginning of period at Mar. 31, 2020	$ 17,598		$ 7	299,689	(281,083)	(1,015)
Balances at beginning of period (in shares) at Mar. 31, 2020			6,830
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock through equity distribution agreement, net of offering costs (in shares)	0
Issuance of common stock from vesting of restricted stock units	$ 0		$ 0	0	0	0
Issuance of common stock from vesting of restricted stock units (in shares)			118
Tax withholding related to vesting of restricted stock units	(131)		$ 0	(131)	0	0
Issuance of common stock under employee stock purchase plan	14		$ 0	14	0	0
Issuance of common stock under employee stock purchase plan (in shares)			11
Stock-based compensation expense	567		$ 0	567	0	0
Net loss	(3,481)		0	0	(3,481)	0
Foreign currency translation adjustments	5		0	0	0	5
Balances at end of period at Jun. 30, 2020	$ 14,572		$ 7	$ 300,139	$ (284,564)	$ (1,010)
Balances at end of period (in shares) at Jun. 30, 2020			6,959

[1] Derived from the Company’s audited consolidated financial statements as of December 31, 2019.