Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 36,088	$ 54,539
Investments	113,895	138,704
Prepaid expenses and other current assets	5,095	5,126
Total current assets	155,078	198,369
Property and equipment, net	32,931	36,125
Long-term investments		36,752
Restricted cash	1,513	1,400
Total assets	189,522	272,646
Current liabilities:
Accounts payable	7,033	7,587
Accrued expenses and other current liabilities	12,513	10,812
Deferred revenue - related party	12,079	12,058
Total current liabilities	31,625	30,457
Lease incentive obligation, net of current portion	8,989	10,730
Deferred rent	2,233	2,072
Deferred revenue, net of current portion - related party	84,847	96,756
Other long-term liabilities	1,129
Total liabilities	128,823	140,015
Commitments and contingencies (Note 11)
Stockholders’ equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized at December 31, 2017 and 2016; no shares issued and outstanding at December 31, 2017 and 2016
Common stock, $0.001 par value; 200,000,000 shares authorized at December 31, 2017 and 2016; 40,571,015 and 40,355,753 shares issued and outstanding at December 31, 2017 and 2016	40	40
Additional paid-in capital	324,376	306,931
Accumulated other comprehensive income (loss)	(146)	(149)
Accumulated deficit	(263,571)	(174,191)
Total stockholders’ equity	60,699	132,631
Total liabilities, convertible preferred stock and stockholders’ equity	$ 189,522	$ 272,646