Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 325,830	$ 306,235
Marketable securities	766,603	212,613
Prepaid expenses and other current assets	12,958	6,227
Receivable from collaborator	18,378
Total current assets	1,123,769	525,075
Property and equipment, net	4,445	4,013
Restricted cash	1,269	849
Total assets	1,129,483	529,937
Current liabilities:
Accounts payable	8,338	9,350
Accrued expenses	39,581	42,601
Total current liabilities	47,919	51,951
Other liabilities	3,801	2,511
Total liabilities	51,720	54,462
Commitments and contingencies (Note 5)
Stockholders’ equity:
Preferred stock, $0.0001 par value per share; 5,000,000 shares authorized at June 30, 2018 and December 31, 2017; no shares issued or outstanding at June 30, 2018 and December 31, 2017
Common stock, $0.0001 par value per share; 120,000,000 shares authorized at June 30, 2018 and December 31, 2017; 46,605,353 and 42,003,894 shares issued at June 30, 2018 and December 31, 2017, respectively; 46,603,839 and 42,002,934 shares outstanding at June 30, 2018 and December 31, 2017, respectively	5	5
Treasury stock, at cost, 1,514 and 960 shares at June 30, 2018 and December 31, 2017, respectively	(211)	(113)
Additional paid-in capital	1,760,137	1,066,059
Accumulated deficit	(682,023)	(590,447)
Accumulated other comprehensive loss	(145)	(29)
Total stockholders’ equity	1,077,763	475,475
Total liabilities and stockholders’ equity	$ 1,129,483	$ 529,937