Consolidated Balance Sheets - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 85,820,000	$ 36,088,000
Investments	0	113,895,000
Prepaid expenses and other current assets	6,845,000	5,095,000
Total current assets	92,665,000	155,078,000
Property and equipment, net	26,294,000	32,931,000
Restricted investments	1,400,000	1,400,000
Restricted cash	113,000	113,000
Total assets	120,472,000	189,522,000
Current liabilities:
Accounts payable	6,415,000	7,033,000
Accrued expenses and other current liabilities	15,207,000	12,513,000
Deferred revenue - related party	20,419,000	12,079,000
Total current liabilities	42,041,000	31,625,000
Lease incentive obligation, net of current portion	7,250,000	8,989,000
Deferred rent	2,216,000	2,233,000
Deferred revenue, net of current portion - related party	116,840,000	84,847,000
Other long-term liabilities	170,000	1,129,000
Total liabilities	168,517,000	128,823,000
Commitments and contingencies (Note 11)
Stockholders’ equity (deficit):
Preferred stock, $0.001 par value; 10,000,000 shares authorized at December 31, 2018 and 2017; no shares issued and outstanding at December 31, 2018 and 2017
Common stock, $0.001 par value; 200,000,000 shares authorized at December 31, 2018 and 2017; 40,936,735 and 40,571,015 shares issued and outstanding at December 31, 2018 and 2017	41,000	40,000
Additional paid-in capital	341,284,000	324,376,000
Accumulated other comprehensive income (loss)		(146,000)
Accumulated deficit	(389,370,000)	(263,571,000)
Total stockholders’ equity (deficit)	(48,045,000)	60,699,000
Total liabilities and stockholders’ equity (deficit)	$ 120,472,000	$ 189,522,000