Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 53,600	$ 85,820
Accounts receivable	6,667
Prepaid expenses and other current assets	7,488	6,845
Total current assets	67,755	92,665
Property and equipment, net	24,571	26,294
Operating lease assets	13,202
Restricted investments	1,400	1,400
Restricted cash	114	113
Total assets	107,042	120,472
Current liabilities:
Accounts payable	3,918	6,415
Accrued expenses and other current liabilities	11,789	15,207
Operating lease liabilities	4,407
Deferred revenue - related party	18,685	20,419
Deferred revenue	2,770
Total current liabilities	41,569	42,041
Operating lease liabilities, net of current portion	19,066
Lease incentive obligation, net of current portion		6,776
Deferred rent		2,216
Deferred revenue, net of current portion - related party	111,959	116,840
Deferred revenue, net of current portion	3,637
Other long-term liabilities	644	644
Total liabilities	176,875	168,517
Commitments and contingencies (Note 11)
Stockholders’ deficit:
Preferred stock, $0.001 par value; 10,000,000 shares authorized at March 31, 2019 and December 31, 2018; no shares issued and outstanding at March 31, 2019 and December 31, 2018
Common stock, $0.001 par value; 200,000,000 shares authorized at March 31, 2019 and December 31, 2018; 41,094,832 and 40,936,735 shares issued and outstanding at March 31, 2019 and December 31, 2018, respectively	41	41
Additional paid-in capital	343,829	341,284
Accumulated deficit	(413,703)	(389,370)
Total stockholders’ deficit	(69,833)	(48,045)
Total liabilities and stockholders’ deficit	$ 107,042	$ 120,472