Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 126,705	$ 190,943
Marketable securities	881,688	731,833
Prepaid expenses and other current assets	26,700	21,919
Total current assets	1,035,093	944,695
Property and equipment, net	9,126	5,643
Restricted cash	2,367	2,367
Right-of-use operating asset	33,771
Other long-term assets	3,793
Total assets	1,084,150	952,705
Current liabilities:
Accounts payable	15,266	34,036
Accrued expenses	86,618	51,994
Operating lease liability, current portion	10,244
Total current liabilities	112,128	86,030
Operating lease liability, net of current portion	26,848
Other liabilities	519	3,704
Total liabilities	139,495	89,734
Commitments and contingencies (Note 5)
Stockholders’ equity:
Preferred stock, $0.0001 par value per share; 5,000,000 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, $0.0001 par value per share; 120,000,000 shares authorized at December 31, 2019 and December 31, 2018; 51,880,227 and 46,891,296 shares issued at December 31, 2019 and December 31, 2018; 51,877,194 and 46,888,263 shares outstanding at December 31, 2019 and December 31, 2018	5	5
Treasury stock, at cost, 3,033 shares at December 31, 2019 and December 31, 2018	(400)	(211)
Additional paid-in capital	2,587,322	1,827,021
Accumulated deficit	(1,643,567)	(963,329)
Accumulated other comprehensive gain (loss)	1,295	(515)
Total stockholders’ equity	944,655	862,971
Total liabilities and stockholders’ equity	$ 1,084,150	$ 952,705