CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 115,566	$ 38,220
Short-term investments	180,230	176,517
Prepaid expenses and other current assets	2,973	6,948
Total current assets	298,769	221,685
Property and equipment, net	41,113	35,637
Restricted cash	1,274	1,772
Total assets	341,156	259,094
Current liabilities:
Accounts payable	8,334	15,732
Accrued expenses and other liabilities	5,306	5,040
Deferred rent	1,161	977
Deferred revenue	690	770
Total current liabilities	15,491	22,519
Non-current liabilities:
Deferred rent, net of current portion	10,326	9,470
Deferred revenue, net of current portion	30,597	30,750
Total liabilities	56,414	62,739
Commitments and contingencies (Note 7)
Stockholders’ equity:
Preferred stock, $0.0001 par value, 10,000,000 shares authorized as of June 30, 2019 and December 31, 2018; no shares issued and outstanding at June 30, 2019 and December 31, 2018
Common stock, $0.0001 par value; 200,000,000 shares authorized as of June 30, 2019 and December 31, 2018; 43,958,295 and 37,509,815 shares issued as of June 30, 2019 and December 31, 2018, respectively; and 43,869,614 and 37,358,526 shares outstanding as of June 30, 2019 and December 31, 2018, respectively	4	3
Additional paid-in capital	430,432	292,187
Accumulated other comprehensive gain (loss)	186	(77)
Accumulated deficit	(145,880)	(95,758)
Total stockholders’ equity	284,742	196,355
Total liabilities and stockholders' equity	$ 341,156	$ 259,094