Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current Assets:
Cash and cash equivalents	$ 47,097	$ 58,856
Marketable securities	249,485	255,203
Accounts receivable	3,591	7,547
Prepaid expenses and other current assets	3,520	3,371
Total current assets	303,693	324,977
Property and equipment, net	16,669	17,061
Operating lease right-of-use assets	21,012
Other assets	2,989	5,277
Total Assets	344,363	347,315
Current Liabilities:
Accounts payable	3,687	2,708
Accrued expenses	7,735	10,742
Current portion of lease liability	4,381
Current portion of deferred revenue	23,431	27,122
Total current liabilities	39,234	40,572
Deferred revenue, net of current portion	25,659	28,810
Long-term lease liability	15,132
Other long-term liabilities		13
Commitments and contingencies
Stockholders’ Equity:
Common stock, $0.0001 par value; 120,000,000 shares authorized; 45,479,098 and 45,224,480 shares issued and outstanding at March 31, 2019 and December 31, 2018, respectively	5	5
Additional paid-in capital	487,559	478,968
Accumulated other comprehensive income (loss)	59	(28)
Accumulated deficit	(223,285)	(201,025)
Total stockholders’ equity	264,338	277,920
Total Liabilities and Stockholders’ Equity	$ 344,363	$ 347,315