Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 5,569	$ 3,169
Investment securities	56,088	72,453
Prepaid expenses and other current assets	1,781	1,310
Total current assets	63,438	76,932
Property, plant and equipment, net	96,026	92,070
Operating lease right-of-use assets, net	1,378
Total assets	160,842	169,002
Current liabilities
Accounts payable	1,513	719
Share-based compensation liability	402	3,018
Accrued liabilities and other current liabilities	4,187	8,353
Current operating lease liabilities	1,320
Total current liabilities	7,422	12,090
Non-current Common Stock Warrant liabilities	7,638	7,441
Non-current operating lease liabilities	352
Total liabilities	15,412	19,531
Commitments and contingencies (Note 11)
Stockholders’ equity
Common stock, $0.0001 par value Authorized: 480.0 million shares at March 31, 2019 and December 31, 2018 Issued and outstanding: 107.0 million shares and 106.9 million shares at March 31, 2019 and December 31, 2018, respectively	11	11
Treasury stock: 71,566 shares and 6,425 shares at March 31, 2019 and December 31, 2018, respectively, at cost	(295)	(35)
Preferred stock, $0.0001 par value Authorized: 0.9 million, after designation of the Series A and Series B Convertible Preferred Stock Issued and outstanding: none at March 31, 2019 and December 31, 2018
Additional paid-in-capital	183,834	180,862
Accumulated deficit	(109,873)	(97,617)
Total stockholders’ equity	73,677	83,221
Total liabilities, Series A and Series B Convertible Preferred Stock and stockholders’ equity	160,842	169,002
Series A Convertible Preferred stock
Current liabilities
Convertible Preferred Stock	43,775	40,091
Series B Convertible Preferred stock
Current liabilities
Convertible Preferred Stock	$ 27,978	$ 26,159