Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 184,270	$ 126,705
Marketable securities	484,267	881,688
Prepaid expenses and other current assets	30,347	26,700
Total current assets	698,884	1,035,093
Property and equipment, net	7,404	9,126
Restricted cash	2,367	2,367
Right-of-use operating asset	26,546	33,771
Other long-term assets	3,427	3,793
Total assets	738,628	1,084,150
Current liabilities:
Accounts payable	4,289	15,266
Accrued expenses	46,756	86,618
Operating lease liability, current portion	8,620	10,244
Total current liabilities	59,665	112,128
Operating lease liability, net of current portion	21,069	26,848
Other liabilities	313	519
Total liabilities	81,047	139,495
Commitments and contingencies (Note 5)
Stockholders’ equity:
Preferred stock, $0.0001 par value per share; 5,000,000 shares authorized at September 30, 2020 and December 31, 2019; no shares issued or outstanding at September 30, 2020 and December 31, 2019
Common stock, $0.0001 par value per share; 120,000,000 shares authorized at September 30, 2020 and December 31, 2019; 52,025,862 and 51,880,227 shares issued at September 30, 2020 and December 31, 2019; 52,022,829 and 51,877,194 shares outstanding at September 30, 2020 and December 31, 2019	5	5
Treasury stock, at cost, 3,033 shares at September 30, 2020 and December 31, 2019	(400)	(400)
Additional paid-in capital	2,669,419	2,587,322
Accumulated deficit	(2,012,389)	(1,643,567)
Accumulated other comprehensive gain	946	1,295
Total stockholders’ equity	657,581	944,655
Total liabilities and stockholders’ equity	$ 738,628	$ 1,084,150