Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 100,731	$ 51,562
Short-term investments	13,983	39,178
Accounts receivable, net of allowance for doubtful accounts of $1,475 and $1,478 at June 30, 2018 and December 31, 2017, respectively	48,476	73,661
Deferred contract acquisition and fulfillment costs, current portion	9,481	0
Prepaid expenses and other current assets	13,212	8,877
Total current assets	185,883	173,278
Long-term investments	3,929	1,102
Property and equipment, net	11,184	8,589
Goodwill	83,164	83,164
Intangible assets, net	16,002	16,640
Deferred contract acquisition and fulfillment costs, non-current portion	22,214	0
Other assets	1,395	1,363
Total assets	323,771	284,136
Current liabilities:
Accounts payable	4,612	2,240
Accrued expenses	21,832	29,728
Deferred revenue, current portion	153,634	155,811
Other current liabilities	1,079	1,706
Total current liabilities	181,157	189,485
Deferred revenue, non-current portion	70,766	68,689
Other long-term liabilities	2,305	1,809
Total liabilities	254,228	259,983
Stockholders’ equity:
Preferred stock, $0.01 par value per share; 10,000,000 shares authorized at June 30, 2018 and December 31, 2017; 0 shares issued at June 30, 2018 and December 31, 2017	0	0
Common stock, $0.01 par value per share; 100,000,000 shares authorized at June 30, 2018 and December 31, 2017; 47,225,844 and 44,540,544 shares issued at June 30, 2018 and December 31, 2017, respectively; 46,739,036 and 44,053,736 shares outstanding at June 30, 2018 and December 31, 2017, respectively	467	441
Treasury stock, at cost, 486,808 shares at June 30, 2018 and December 31, 2017	(4,764)	(4,764)
Additional paid-in-capital	513,598	463,428
Accumulated other comprehensive loss	(24)	(39)
Accumulated deficit	(439,734)	(434,913)
Total stockholders’ equity	69,543	24,153
Total liabilities and stockholders’ equity	$ 323,771	$ 284,136