Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 30,708	$ 49,826
Marketable securities	198,818	193,482
Interest receivable	373	240
Accounts receivable	3,575	3,343
Prepaid expenses and other current assets	2,802	1,506
Total current assets	236,276	248,397
Marketable securities, non-current	4,986	1,012
Property and equipment, net	33,601	31,066
Goodwill	1,585	1,585
Restricted cash and other non-current assets	4,720	4,681
Total assets	281,168	286,741
Current liabilities:
Accounts payable and accrued liabilities	10,970	11,035
Accrued compensation and employee benefits	3,211	5,479
Deferred revenues	35,209	28,345
Total current liabilities	49,390	44,859
Deferred revenues, non-current	23,964	29,244
Build-to-suit lease obligation	25,449	24,738
Total liabilities	98,803	98,841
Commitments and contingencies
Stockholders' equity:
Common stock, $0.01 par value; 160,000,000 shares authorized, 87,041,208 and 85,598,534 shares issued and outstanding at March 31, 2018 and December 31, 2017, respectively	870	856
Additional paid-in capital	696,429	682,809
Accumulated deficit	(514,549)	(495,479)
Accumulated other comprehensive loss	(385)	(286)
Total stockholders' equity	182,365	187,900
Total liabilities and stockholders' equity	$ 281,168	$ 286,741