Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 55,852	$ 75,561
Marketable securities	229,373	244,200
Accounts receivable	8,372	8,587
Prepaid expenses	6,292	5,734
Other current assets	3,995	3,831
Total current assets	303,884	337,913
Marketable securities	159,083	150,819
Accounts receivable	22,758	23,012
Property and equipment, net	23,140	28,702
Operating lease right-of-use assets	6,858
Restricted cash	1,053	1,053
Other assets	2,255	2,315
Total assets	519,031	543,814
Current liabilities
Accounts payable	4,204	4,412
Accrued expenses and other current liabilities	14,189	17,164
Deferred revenue	600	600
Operating lease liabilities	2,397
Total current liabilities	21,390	22,176
Deferred revenue	3,333	3,333
Operating lease liabilities	5,483
Deferred rent		1,098
Financing lease obligations		5,854
Other liabilities	1,772	2,505
Total liabilities	31,978	34,966
Commitments and contingencies (Note 6)
Stockholders’ equity
Preferred stock; $0.0001 par value; 10,000 shares authorized, and no shares issued and outstanding at March 31, 2019 and December 31, 2018
Common stock; $0.0001 par value; 100,000 shares authorized at March 31, 2019 and December 31, 2018; 36,611 and 36,120 shares issued and outstanding at March 31, 2019 and December 31, 2018, respectively	4	4
Additional paid-in capital	602,425	592,580
Accumulated other comprehensive loss	(59)	(720)
Accumulated deficit	(115,317)	(83,016)
Total stockholders’ equity	487,053	508,848
Total liabilities and stockholders’ equity	$ 519,031	$ 543,814