Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 55,069	$ 42,007
Short-term investments	93,901	36,741
Accounts receivable, net of allowance for doubtful accounts of $569 and $289	68,782	58,587
Prepaid expenses and other current assets	5,079	5,440
Total current assets	222,831	142,775
Long-term assets
Property and equipment, net of accumulated depreciation of $17,091 and $12,774	10,437	12,827
Long-term investments		38,446
Other long-term assets	983	734
Total assets	234,251	194,782
Current liabilities
Accounts payable	5,598	3,574
Accrued payroll and other expenses	16,481	14,073
Deferred revenue	116,831	97,885
Deferred rent	892	799
Capital leases	21	43
Total current liabilities	139,823	116,374
Long-term liabilities
Deferred revenue, net of current portion	2,470	2,254
Deferred rent, net of current portion	3,483	4,360
Capital leases, net of current portion	26	51
Asset retirement obligation	199	175
Total liabilities	146,001	123,214
Commitments and contingencies (Note 11)
Stockholders’ equity
Class A and Class B Common stock	4	4
Additional paid-in capital	314,301	271,982
Accumulated other comprehensive loss	(110)	(94)
Accumulated deficit	(225,945)	(200,324)
Total stockholders’ equity	88,250	71,568
Total liabilities and stockholders' equity	$ 234,251	$ 194,782