Consolidated Balance Sheets - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 320,078,000	$ 186,753,000
Marketable securities	111,192,000	0
Prepaid expenses and other current assets	3,418,000	1,738,000
Total current assets	434,688,000	188,491,000
Property and equipment, net	1,049,000	286,000
Restricted cash	564,000	39,000
Deferred offering costs		200,000
Total assets	436,301,000	189,016,000
Current liabilities:
Accounts payable	5,237,000	5,159,000
Accrued expenses	17,093,000	10,148,000
Total current liabilities	22,330,000	15,307,000
Other liabilities	234,000	14,000
Total liabilities	22,564,000	15,321,000
Commitments and contingencies (Note 5)
Stockholders’ equity:
Preferred stock, $0.0001 par value per share; 5,000,000 shares authorized at September 30, 2016 and December 31, 2015, respectively; no shares issued or outstanding at September 30, 2016 and December 31, 2015, respectively
Common stock, $0.0001 par value per share; 120,000,000 shares authorized at September 30, 2016 and December 31, 2015, respectively; 37,165,124 and 28,823,549 shares issued and outstanding at September 30, 2016 and December 31, 2015, respectively	4,000	3,000
Additional paid-in capital	678,194,000	335,032,000
Accumulated deficit	(264,426,000)	(161,340,000)
Accumulated other comprehensive items	(35,000)
Total stockholders’ equity	413,737,000	173,695,000
Total liabilities and stockholders’ equity	$ 436,301,000	$ 189,016,000