Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Revenues	$ 24,291	$ 3,708	$ 17,347
Costs and expenses
Research and development (including stock compensation expense of $1,609, $1,232 and $1,192 in 2018, 2017 and 2016, respectively)	38,656	27,841	24,838
General and administrative (including stock compensation expense of $2,240, $1,812 and $1,676 in 2018, 2017 and 2016, respectively)	10,442	8,466	7,835
Depreciation	855	684	382
Total costs and expenses	49,953	36,991	33,055
Gain from insurance proceeds, net	617	0	682
Loss from operations	(25,045)	(33,283)	(15,026)
Income (expense) from change in fair value of warrants, net	0	728	(557)
Other income, net	762	314	209
Loss before income taxes	(24,283)	(32,241)	(15,374)
Income tax benefit	0	0	37
Net loss and comprehensive loss	$ (24,283)	$ (32,241)	$ (15,337)
Net loss per common share, basic and diluted (in dollars per share)	$ (0.18)	$ (0.29)	$ (0.18)
Weighted average shares outstanding, basic and diluted (in shares)	136,641	112,053	84,715
Royalty and other contract revenue
Revenues
Revenues	$ 1,461	$ 1,925	$ 0
Grant revenue
Revenues
Revenues	554	865	1,109
Healios License Agreement | Contract revenue from Healios
Revenues
Revenues	$ 22,276	$ 918	$ 16,238