Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 49,296	$ 85,820
Investments	34,492
Prepaid expenses and other current assets	4,073	6,845
Accounts receivable	1,717
Total current assets	89,578	92,665
Property and equipment, net	21,160	26,294
Operating lease assets	11,899
Restricted investments	1,400	1,400
Restricted cash	114	113
Total assets	124,151	120,472
Current liabilities:
Accounts payable	4,455	6,415
Accrued expenses and other current liabilities	10,522	15,207
Operating lease liabilities	4,335
Deferred revenue - related party	21,135	20,419
Deferred revenue	1,790
Total current liabilities	42,237	42,041
Operating lease liabilities, net of current portion	16,844
Lease incentive obligation, net of current portion		6,776
Deferred rent		2,216
Deferred revenue, net of current portion - related party	94,215	116,840
Deferred revenue, net of current portion	2,410
Other long-term liabilities	664	644
Total liabilities	156,370	168,517
Commitments and contingencies (Note 12)
Stockholders’ deficit:
Preferred stock, $0.001 par value; 10,000,000 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; 200,000,000 shares authorized at September 30, 2019 and December 31, 2018; 69,993,952 and 40,936,735 shares issued and outstanding at September 30, 2019 and December 31, 2018, respectively	70	41
Additional paid-in capital	408,575	341,284
Accumulated other comprehensive income	7
Accumulated deficit	(440,871)	(389,370)
Total stockholders’ deficit	(32,219)	(48,045)
Total liabilities and stockholders’ deficit	$ 124,151	$ 120,472