Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 47,194	$ 36,088
Investments	75,000	113,895
Prepaid expenses and other current assets	4,260	5,095
Total current assets	126,454	155,078
Property and equipment, net	31,466	32,931
Restricted cash	1,513	1,513
Total assets	159,433	189,522
Current liabilities:
Accounts payable	5,418	7,033
Accrued expenses and other current liabilities	11,873	12,513
Deferred revenue - related party	17,859	12,079
Total current liabilities	35,150	31,625
Lease incentive obligation, net of current portion	8,554	8,989
Deferred rent	2,234	2,233
Deferred revenue, net of current portion - related party	102,333	84,847
Other long-term liabilities	1,129	1,129
Total liabilities	149,400	128,823
Commitments and contingencies (Note 10)
Stockholders’ equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized at March 31, 2018 and December 31, 2017; no shares issued and outstanding at March 31, 2018 and December 31, 2017
Common stock, $0.001 par value; 200,000,000 shares authorized at March 31, 2018 and December 31, 2017; 40,652,668 and 40,571,015 shares issued and outstanding at March 31, 2018 and December 31, 2017, respectively	40	40
Additional paid-in capital	328,446	324,376
Accumulated other comprehensive loss	(106)	(146)
Accumulated deficit	(318,347)	(263,571)
Total stockholders’ equity	10,033	60,699
Total liabilities and stockholders’ equity	$ 159,433	$ 189,522