Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 46,859	$ 31,530
Marketable securities, current	108,947	137,522
Prepaid expenses and other current assets	6,675	2,738
Total current assets	162,481	171,790
Property, Plant and Equipment, Net	12,771	10,283
Deposits and other non-current assets	1,149	1,304
Marketable securities, non-current	628	1,100
Total assets	177,029	184,477
Current liabilities:
Accounts payable	1,038	1,020
Accrued expenses	9,788	11,497
Deferred revenue, current portion	20,847	3,380
Total current liabilities	31,673	15,897
Deferred rent	5,710	5,337
Deferred revenue, net of current portion	92,199	28,180
Other non-current liabilities	1,001	1,012
Total liabilities	130,583	50,426
Commitments and contingencies (see note 7)
Stockholders’ equity:
Preferred stock, $0.001 par value: 5,000,000 shares authorized; no shares issued and outstanding at December 31, 2018 and 2017
Common stock, $0.001 par value: 120,000,000 shares authorized; 32,364,895 and 31,572,044 shares issued and outstanding at December 31, 2018 and 2017, respectively	32	32
Additional paid-in capital	315,598	295,019
Accumulated other comprehensive loss	(133)	(287)
Accumulated deficit	(269,051)	(160,713)
Total stockholders’ equity	46,446	134,051
Total liabilities and stockholders’ equity	$ 177,029	$ 184,477