Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 55,142	$ 75,561
Marketable securities	286,354	244,200
Accounts receivable	9,679	8,587
Prepaid expenses	6,036	5,734
Other current assets	2,281	3,831
Total current assets	359,492	337,913
Marketable securities	108,194	150,819
Accounts receivable	23,955	23,012
Property and equipment, net	27,330	28,702
Operating lease right-of-use assets	5,904
Restricted cash	1,053	1,053
Other assets	3,211	2,315
Total assets	529,139	543,814
Current liabilities
Accounts payable	5,851	4,412
Accrued expenses and other current liabilities	16,534	17,164
Deferred revenue		600
Operating lease liabilities	2,276
Total current liabilities	24,661	22,176
Deferred revenue	3,333	3,333
Operating lease liabilities	4,654
Deferred rent		1,098
Financing lease obligations		5,854
Other liabilities	1,899	2,505
Total liabilities	34,547	34,966
Commitments and contingencies (Note 7)
Stockholders’ equity
Preferred stock; $0.0001 par value; 10,000 shares authorized, and no shares issued and outstanding at June 30, 2019 and December 31, 2018
Common stock; $0.0001 par value; 100,000 shares authorized at June 30, 2019 and December 31, 2018; 36,752 and 36,120 shares issued and outstanding at June 30, 2019 and December 31, 2018, respectively	4	4
Additional paid-in capital	610,891	592,580
Accumulated other comprehensive income (loss)	471	(720)
Accumulated deficit	(116,774)	(83,016)
Total stockholders’ equity	494,592	508,848
Total liabilities and stockholders’ equity	$ 529,139	$ 543,814