Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 166,185	$ 190,943
Marketable securities	1,070,364	731,833
Prepaid expenses and other current assets	27,021	21,919
Total current assets	1,263,570	944,695
Property and equipment, net	8,363	5,643
Restricted cash	2,367	2,367
Right of use operating asset	37,224
Other long-term assets	4,023
Total assets	1,315,547	952,705
Current liabilities:
Accounts payable	12,431	34,036
Accrued expenses	58,912	51,994
Other current liabilities	7,610
Total current liabilities	78,953	86,030
Long-term lease operating liability, net of current portion	33,309
Other long-term liabilities	410	3,704
Total liabilities	112,672	89,734
Commitments and contingencies (Note 5)
Stockholders’ equity:
Preferred stock, $0.0001 par value per share; 5,000,000 shares authorized at June 30, 2019 and December 31, 2018; no shares issued or outstanding at June 30, 2019 and December 31, 2018
Common stock, $0.0001 par value per share; 120,000,000 shares authorized at June 30, 2019 and December 31, 2018; 51,472,137 and 46,891,296 shares issued at June 30, 2019 and December 31, 2018; 51,469,104 and 46,888,263 shares outstanding at June 30, 2019 and December 31, 2018	5	5
Treasury stock, at cost, 3,033 shares at June 30, 2019 and December 31, 2018	(400)	(211)
Additional paid-in capital	2,496,651	1,827,021
Accumulated deficit	(1,294,956)	(963,329)
Accumulated other comprehensive gain (loss)	1,575	(515)
Total stockholders’ equity	1,202,875	862,971
Total liabilities and stockholders’ equity	$ 1,315,547	$ 952,705