Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 253,123	$ 306,235
Marketable securities	768,278	212,613
Prepaid expenses and other current assets	18,511	6,227
Total current assets	1,039,912	525,075
Property and equipment, net	5,168	4,013
Restricted cash	1,919	849
Total assets	1,046,999	529,937
Current liabilities:
Accounts payable	5,879	9,350
Accrued expenses	48,647	42,601
Total current liabilities	54,526	51,951
Other liabilities	3,968	2,511
Total liabilities	58,494	54,462
Commitments and contingencies (Note 5)
Stockholders’ equity:
Preferred stock, $0.0001 par value per share; 5,000,000 shares authorized at September 30, 2018 and December 31, 2017; no shares issued or outstanding at September 30, 2018 and December 31, 2017
Common stock, $0.0001 par value per share; 120,000,000 shares authorized at September 30, 2018 and December 31, 2017; 46,832,103 and 42,003,894 shares issued at September 30, 2018 and December 31, 2017, respectively; 46,830,589 and 42,002,934 shares outstanding at September 30, 2018 and December 31, 2017, respectively	5	5
Treasury stock, at cost, 1,514 and 960 shares at September 30, 2018 and December 31, 2017, respectively	(211)	(113)
Additional paid-in capital	1,793,909	1,066,059
Accumulated deficit	(804,941)	(590,447)
Accumulated other comprehensive loss	(257)	(29)
Total stockholders’ equity	988,505	475,475
Total liabilities and stockholders’ equity	$ 1,046,999	$ 529,937