CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 77,559	$ 38,220
Short-term investments	192,113	176,517
Prepaid expenses and other current assets	4,407	6,948
Total current assets	274,079	221,685
Property and equipment, net	41,406	35,637
Restricted cash	1,274	1,772
Total assets	316,759	259,094
Current liabilities:
Accounts payable	8,798	15,732
Accrued expenses and other liabilities	7,818	5,040
Deferred rent	1,292	977
Deferred revenue	774	770
Total current liabilities	18,682	22,519
Non-current liabilities:
Deferred rent, net of current portion	9,888	9,470
Deferred revenue, net of current portion	30,367	30,750
Total liabilities	58,937	62,739
Commitments and contingencies (Note 7)
Stockholders’ equity:
Preferred stock, $0.0001 par value, 10,000,000 shares authorized as of September 30, 2019 and December 31, 2018; no shares issued and outstanding at September 30, 2019 and December 31, 2018
Common stock, $0.0001 par value; 200,000,000 shares authorized as of September 30, 2019 and December 31, 2018; 44,028,647 and 37,509,815 shares issued as of September 30, 2019 and December 31, 2018, respectively; and 43,956,070 and 37,358,526 shares outstanding as of September 30, 2019 and December 31, 2018, respectively	4	3
Additional paid-in capital	433,071	292,187
Accumulated other comprehensive gain (loss)	254	(77)
Accumulated deficit	(175,507)	(95,758)
Total stockholders’ equity	257,822	196,355
Total liabilities and stockholders' equity	$ 316,759	$ 259,094