Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Consolidated entity, excluding related party	Consolidated entity, excluding related party Common Stock	Consolidated entity, excluding related party Additional Paid-in Capital	Healios	Healios Common Stock	Healios Additional Paid-in Capital
Preferred stock shares, beginning balance (in shares) at Dec. 31, 2016		0
Common stock, beginning balance (in shares) at Dec. 31, 2016			86,629,302
Beginning balance at Dec. 31, 2016	$ 11,181	$ 0	$ 87	$ 329,373	$ (318,279)
Stock-based compensation	3,154			3,154
Issuance of common stock from warrant exercises (in shares)			1,843,363
Issuance of common stock from warrant exercises	1,862		$ 2	1,860
Issuance of common stock, net of issuance costs (in shares)							33,172,300
Issuance of common stock, net of issuance costs						$ 39,813	$ 33	$ 39,780
Issuance of common stock under equity compensation plans (in shares)			432,488
Issuance of common stock under equity compensation plans	(283)			(283)
Net and comprehensive loss	(32,241)				(32,241)
Preferred stock shares, ending balance (in shares) at Dec. 31, 2017		0
Common stock, ending balance (in shares) at Dec. 31, 2017			122,077,453
Ending balance at Dec. 31, 2017	23,376	$ 0	$ 122	373,884	(350,630)
Stock-based compensation	3,849			3,849
Issuance of warrant to Healios at fair value									$ 1,080		$ 1,080
Issuance of common stock, net of issuance costs (in shares)							9,658,582			12,000,000
Issuance of common stock, net of issuance costs						16,628	$ 9	16,619	$ 20,995	$ 12	$ 20,983
Issuance of common stock under equity compensation plans (in shares)			556,704
Issuance of common stock under equity compensation plans	(400)		$ 1	(401)
Net and comprehensive loss	$ (24,283)				(24,283)
Preferred stock shares, ending balance (in shares) at Dec. 31, 2018	0	0
Common stock, ending balance (in shares) at Dec. 31, 2018	144,292,739		144,292,739
Ending balance at Dec. 31, 2018	$ 43,116	$ 0	$ 144	416,014	(373,042)
Stock-based compensation	4,851			4,851
Issuance of common stock, net of issuance costs (in shares)							14,825,000
Issuance of common stock, net of issuance costs						$ 20,284	$ 15	$ 20,269
Issuance of common stock under equity compensation plans (in shares)			673,846
Issuance of common stock under equity compensation plans	(398)		$ 1	(399)
Net and comprehensive loss	$ (44,582)				(44,582)
Preferred stock shares, ending balance (in shares) at Dec. 31, 2019	0	0
Common stock, ending balance (in shares) at Dec. 31, 2019	159,791,585		159,791,585
Ending balance at Dec. 31, 2019	$ 23,271	$ 0	$ 160	$ 440,735	$ (417,624)