CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 144,517	$ 91,898
Investments	96,874	191,389
Prepaid expenses and other current assets	4,491	5,979
Total current assets	245,882	289,266
Operating lease, right-of-use-asset	43,998	46,559
Property, plant and equipment, net	56,383	56,924
Restricted cash	1,735	1,735
Other assets	329	357
Total assets	348,327	394,841
Current liabilities:
Accounts payable	7,626	7,178
Accrued expenses and other current liabilities	10,291	16,042
Operating lease liabilities	9,433	10,540
Total current liabilities	27,350	33,760
Long-term debt, net of discount	49,683	49,596
Other long-term liabilities	371	405
Operating lease liabilities, net of current portion	35,766	36,867
Total liabilities	113,170	120,628
Commitments and contingencies (see Note 9)
Stockholders' equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized at March 31, 2020 and December 31, 2019; no shares issued or outstanding at March 31, 2020 and December 31, 2019
Common stock, $0.001 par value; 150,000,000 shares authorized at March 31, 2020 and December 31, 2019; 80,429,966 and 80,016,245 shares issued and outstanding at March 31, 2020 and December 31, 2019, respectively	80	80
Additional paid-in capital	595,772	586,798
Accumulated other comprehensive income	531	75
Accumulated deficit	(361,226)	(312,740)
Total stockholders' equity	235,157	274,213
Total liabilities and stockholders' equity	$ 348,327	$ 394,841