Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 4,543	$ 3,169
Investment securities	52,573	72,453
Prepaid expenses and other current assets	1,755	1,310
Total current assets	58,871	76,932
Property, plant and equipment, net	104,198	92,070
Operating lease right-of-use assets, net	1,608
Total assets	164,677	169,002
Current liabilities
Accounts payable	1,856	719
Share-based compensation liability	182	3,018
Accrued liabilities and other current liabilities	4,789	8,353
Current operating lease liabilities	1,784
Total current liabilities	8,611	12,090
Non-current common stock warrant liabilities	11,216	7,441
Non-current operating lease liabilities	273
Total liabilities	20,100	19,531
Commitments and contingencies (Note 11)
Stockholders’ equity
Common stock, $0.0001 par value Authorized: 480.0 million shares at June 30, 2019 and December 31, 2018 Issued and outstanding: 107.2 million shares and 106.9 million shares at June 30, 2019 and December 31, 2018, respectively	11	11
Treasury stock: 103,198 shares and 6,425 shares at June 30, 2019 and December 31, 2018, respectively, at cost	(466)	(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 June 30, 2019 and December 31, 2018
Additional paid-in-capital	170,374	180,862
Accumulated deficit	(116,592)	(97,617)
Total stockholders’ equity	53,327	83,221
Total liabilities, series A and series B convertible preferred stock and stockholders’ equity	164,677	169,002
Series A convertible preferred stock
Current liabilities
Convertible preferred stock	44,263	40,091
Series B convertible preferred stock
Current liabilities
Convertible preferred stock	$ 46,987	$ 26,159