Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current Assets:
Cash and cash equivalents	$ 57,226	$ 58,856
Marketable securities	222,500	255,203
Accounts receivable	4,620	7,547
Prepaid expenses and other current assets	5,135	3,371
Total current assets	289,481	324,977
Marketable securities - noncurrent	4,746
Property and equipment, net	17,996	17,061
Operating lease right-of-use assets	19,137
Other assets	2,920	5,277
Total Assets	334,280	347,315
Current Liabilities:
Accounts payable	3,941	2,708
Accrued expenses	13,273	10,742
Current portion of operating lease liability	5,745
Current portion of deferred revenue	12,674	27,122
Total current liabilities	35,633	40,572
Deferred revenue, net of current portion	16,136	28,810
Long-term operating lease liability	12,630
Other long-term liabilities		13
Commitments and contingencies (Note 8)
Stockholders’ Equity:
Common stock, $0.0001 par value; 120,000,000 shares authorized; 50,198,044 and 45,224,480 shares issued and outstanding at December 31, 2019 and 2018, respectively	5	5
Additional paid-in capital	570,493	478,968
Accumulated other comprehensive income (loss)	261	(28)
Accumulated deficit	(300,878)	(201,025)
Total stockholders’ equity	269,881	277,920
Total Liabilities and Stockholders’ Equity	$ 334,280	$ 347,315