Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 259,181	$ 190,943
Marketable securities	863,069	731,833
Prepaid expenses and other current assets	30,413	21,919
Total current assets	1,152,663	944,695
Property and equipment, net	9,365	5,643
Restricted cash	2,367	2,367
Right-of-use operating asset	35,514
Other long-term assets	3,818
Total assets	1,203,727	952,705
Current liabilities:
Accounts payable	5,041	34,036
Accrued expenses	78,127	51,994
Other current liabilities	7,788
Total current liabilities	90,956	86,030
Long-term lease operating liability, net of current portion	31,360
Other long-term liabilities	340	3,704
Total liabilities	122,656	89,734
Commitments and contingencies (Note 5)
Stockholders’ equity:
Preferred stock, $0.0001 par value per share; 5,000,000 shares authorized at September 30, 2019 and December 31, 2018; no shares issued or outstanding at September 30, 2019 and December 31, 2018
Common stock, $0.0001 par value per share; 120,000,000 shares authorized at September 30, 2019 and December 31, 2018; 51,819,025 and 46,891,296 shares issued at September 30, 2019 and December 31, 2018; 51,815,992 and 46,888,263 shares outstanding at September 30, 2019 and December 31, 2018	5	5
Treasury stock, at cost, 3,033 shares at September 30, 2019 and December 31, 2018	(400)	(211)
Additional paid-in capital	2,554,603	1,827,021
Accumulated deficit	(1,474,914)	(963,329)
Accumulated other comprehensive gain (loss)	1,777	(515)
Total stockholders’ equity	1,081,071	862,971
Total liabilities and stockholders’ equity	$ 1,203,727	$ 952,705