Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 485,819	$ 238,183
Marketable securities	112,901	218,957
Accounts receivable	1,865	418
Prepaid expenses and other current assets	9,541	6,286
Total current assets	610,126	463,844
Property and equipment, net	12,895	10,887
Right-of-use assets	28,569	28,761
Restricted cash and other non-current assets	3,891	5,393
Total assets	655,481	508,885
Current liabilities:
Accounts payable	6,339	5,843
Accrued expenses	10,194	22,120
Deferred revenue, current	40,940	23,514
Operating lease liabilities	6,650	5,804
Other current liabilities	4,027	2,682
Total current liabilities	68,150	59,963
Operating lease liabilities, net of current portion	22,153	23,277
Deferred revenue, net of current portion	138,406	163,207
Other non-current liabilities		1
Total liabilities	228,709	246,448
Stockholders' equity
Preferred stock, $0.0001 par value per share: 5,000,000 shares authorized; no shares issued or outstanding
Common stock, $0.0001 par value per share: 195,000,000 shares authorized; 62,265,649 and 54,533,798 shares issued, and 62,103,649 and 54,355,798 shares outstanding at June 30, 2020 and December 31, 2019, respectively	6	5
Additional paid-in capital	1,037,100	811,546
Accumulated other comprehensive income	183	107
Accumulated deficit	(610,517)	(549,221)
Total stockholders' equity	426,772	262,437
Total liabilities and stockholders' equity	$ 655,481	$ 508,885