Consolidated Balance Sheets - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 58,856,000	$ 340,678,000
Marketable securities	255,203,000	0
Accounts receivable	7,547,000	10,471,000
Prepaid expenses and other current assets	3,371,000	3,681,000
Total current assets	324,977,000	354,830,000
Property and equipment, net	17,061,000	15,272,000
Other assets	5,277,000	6,133,000
Total Assets	347,315,000	376,235,000
Current Liabilities:
Accounts payable	2,708,000	2,172,000
Accrued expenses	10,742,000	7,999,000
Current portion of deferred revenue	27,122,000	21,188,000
Total current liabilities	40,572,000	31,359,000
Deferred revenue, net of current portion	28,810,000	44,111,000
Other long-term liabilities	13,000	168,000
Commitments and contingencies (Note 6)
Stockholders’ Equity:
Common stock, $0.0001 par value; 120,000,000 shares authorized; 45,224,480 and 42,384,623 shares issued and outstanding at December 31, 2018 and 2017, respectively	5,000	4,000
Additional paid-in capital	478,968,000	421,706,000
Accumulated other comprehensive loss	(28,000)
Accumulated deficit	(201,025,000)	(121,113,000)
Total stockholders’ equity	277,920,000	300,597,000
Total Liabilities and Stockholders’ Equity	$ 347,315,000	$ 376,235,000