CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 91,898	$ 307,064
Investments	191,389	96,987
Prepaid expenses and other current assets	5,979	9,737
Restricted cash		622
Total current assets	289,266	414,410
Operating lease, right-of-use-asset	46,559
Property, plant and equipment, net	56,924	62,796
Restricted cash	1,735	1,735
Other assets	357	168
Total assets	394,841	479,109
Current liabilities:
Accounts payable	7,178	7,886
Accrued expenses and other current liabilities	16,042	12,118
Operating lease liabilities	10,540
Total current liabilities	33,760	20,004
Long-term debt, net of discount	49,596	24,347
Other long-term liabilities	405	309
Operating lease liabilities, net of current portion	36,867
Lease financing obligation		41,441
Total liabilities	120,628	86,101
Commitments and contingencies (see Note 12)
Stockholders' equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized at December 31, 2019 and December 31, 2018; no shares issued or outstanding at December 31, 2019 and December 31, 2018
Common stock, $0.001 par value; 150,000,000 shares authorized at December 31, 2019 and December 31, 2018; 80,016,245 and 79,234,853 shares issued and outstanding at December 31, 2019 and December 31, 2018, respectively	80	79
Additional paid-in capital	586,798	543,040
Accumulated other comprehensive income (loss)	75	(29)
Accumulated deficit	(312,740)	(150,082)
Total stockholders' equity	274,213	393,008
Total liabilities and stockholders' equity	$ 394,841	$ 479,109