Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 70,156	$ 187,335
Available for sale securities	247,636	73,008
Accounts receivable	34,216	33,823
Prepaid expenses and other current assets	6,348	2,155
Total current assets	358,356	296,321
Property and equipment, net	3,617	2,612
Other assets	2,274	1,283
Total assets	364,247	300,216
Current liabilities:
Accounts payable	6,998	2,039
Accrued expenses	52,441	30,261
Short-term deferred revenue	84,910	81,968
Total current liabilities	144,349	114,268
Deferred rent, net of current portion	2,588	2,480
Deferred revenue, net of current portion	97,957	115,321
Other non-current liabilities	22	27
Total liabilities	244,916	232,096
Commitments and contingencies (Note 10)
Stockholders' equity:
Preferred stock $0.00001 par value, 25,000,000 shares authorized at December 31, 2017 and 2016; 0 shares issued and outstanding at December 31, 2017 and 2016
Common stock: $0.00001 par value; 175,000,000 shares authorized at December 31, 2017 and 2016; 47,612,619 and 38,615,709 shares issued and outstanding at December 31, 2017 and 2016, respectively	0	0
Additional paid-in capital	493,823	365,298
Accumulated other comprehensive income (loss)	(442)	(42)
Accumulated deficit	(374,050)	(297,136)
Total stockholders' equity	119,331	68,120
Total liabilities and stockholders' equity	$ 364,247	$ 300,216