Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 82,640	$ 46,859
Marketable securities, current	224,760	108,947
Collaboration receivable	11,733
Unbilled accounts receivable	2,300
Prepaid expenses and other current assets	6,164	6,675
Total current assets	327,597	162,481
Property and equipment, net	15,292	12,771
Deposits and other non-current assets	1,976	1,149
Marketable securities, non-current	2,024	628
Operating lease, right-of-use asset	29,331
Total assets	376,220	177,029
Current liabilities:
Accounts payable	4,026	1,038
Accrued expenses	16,588	9,788
Other current liabilities	3,016
Deferred revenue, current portion	56,542	20,847
Total current liabilities	80,172	31,673
Deferred revenue, non-current	155,093	92,199
Other non-current liabilities	32,799	6,711
Total liabilities	268,064	130,583
Commitments and contingencies (see note 8)
Stockholders' equity:
Preferred stock $0.001 par value: 5,000,000 shares authorized at September 30, 2019 and December 31, 2018; no shares issued and outstanding at September 30, 2019 and December 31, 2018
Common stock, $0.001 par value: 120,000,000 shares authorized at September 30, 2019 and December 31, 2018; 36,828,123 and 32,364,895 shares issued and outstanding at September 30, 2019 and December 31, 2018, respectively	37	32
Additional paid-in capital	408,208	315,598
Accumulated other comprehensive loss	(15)	(133)
Accumulated deficit	(300,074)	(269,051)
Total stockholders' equity	108,156	46,446
Total liabilities and stockholders' equity	$ 376,220	$ 177,029