Quarterly report pursuant to Section 13 or 15(d)

Offerings of Common Stock and Warrants and At-the-Market Offering Program (Details)

Offerings of Common Stock and Warrants and At-the-Market Offering Program (Details) - USD ($) $ / shares in Units, $ in Thousands							3 Months Ended	9 Months Ended		30 Months Ended
	Oct. 27, 2017	Oct. 21, 2016	Oct. 18, 2016	Apr. 22, 2016	Apr. 19, 2016	Aug. 28, 2015	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Oct. 26, 2017	Aug. 31, 2017	Mar. 31, 2017
Common stock, par value (in dollars per share)	$ 0.001						$ 0.001	$ 0.001		$ 0.001			$ 0.001
Reduction of warrants to purchase common stock (as a percent)	19.00%
Number of common stock shares available to accredited investors			3,600,000
Share price of common stock sold (in dollars per share)			$ 1.20
Loss on adjustment of exercise price							$ 84	$ 741
Net proceeds from offering of common stock and warrants		$ 6,800		$ 13,100				8,293	$ 19,886
Number of common stock shares available in public offering					2,700,000
Beneficial ownership of common stock resulting from purchase of stock in public offering (as a percent)					4.99%
Number of warrants or shares of common stock to be sold to purchase common stock					2
Aggregate offering price for at-the-market offering program								$ 9,600
Common stock sold (in shares)							3,400,000	9,200,000		16,500,000
Net proceeds from sale of the common stock, after deducting fees and other offering expenses (in dollars)							$ 2,600	$ 6,500		$ 19,300
Common stock commissions paid							100	200		$ 600
Maximum
Aggregate offering price for at-the-market offering program						$ 30,000
Series A Warrants
Number of shares of common stock that could be purchased with warrants					4,100,000						1,928,750
Exercise price (in dollars per share)			$ 1.34		$ 3.50						$ 0.90	$ 0.60
Loss on adjustment of exercise price							$ 100	$ 700
Number of warrants or shares of common stock to be sold to purchase common stock					1
Number of shares of common stock purchased with each warrant					1
Length of time from issue date until warrants are exercisable					6 months
Length of time from exercise date until warrants expire					5 years
Outstanding warrants (in shares)							8,478,750	8,478,750		8,478,750
Net proceeds from sale of the common stock, after deducting fees and other offering expenses (in dollars)	$ 1,700
Series A Warrants \| Maximum
Number of shares of common stock that could be purchased with warrants			6,300,000
Series B Warrants
Number of shares of common stock that could be purchased with warrants			2,700,000
Exercise price (in dollars per share)			$ 1.20		$ 3.48
Exercise price pre-funded at closing (in dollars per share)			1.19
Exercise price, payable upon exercise (in dollars per share)			$ 0.01
Number of warrants or shares of common stock to be sold to purchase common stock					2
Length of time from exercise date until warrants expire					9 months
Outstanding warrants (in shares)							0	0		0
Series B Warrants \| Maximum
Number of shares of common stock that could be purchased with warrants					5,500,000