Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 126,569	$ 99,565
Short-term investments	119,138	159,210
Accounts receivable, net of allowance for doubtful accounts of $1,622 and $1,624 at June 30, 2019 and December 31, 2018, respectively	69,289	74,935
Deferred contract acquisition and fulfillment costs, current portion	13,851	12,321
Prepaid expenses and other current assets	15,416	9,746
Total current assets	344,263	355,777
Long-term investments	18,680	44,892
Property and equipment, net	51,860	17,523
Operating lease right-of-use assets	59,417	0
Deferred contract acquisition and fulfillment costs, non-current portion	29,275	27,634
Goodwill	97,866	88,420
Intangible assets, net	29,726	23,955
Other assets	5,192	1,168
Total assets	636,279	559,369
Current liabilities:
Accounts payable	12,975	7,048
Accrued expenses	33,069	37,376
Operating lease liabilities, current portion	6,057	0
Deferred revenue, current portion	199,048	189,855
Other current liabilities	126	707
Total current liabilities	251,275	234,986
Convertible senior notes, net	179,791	174,688
Operating lease liabilities, non-current portion	71,722	0
Deferred revenue, non-current portion	44,944	58,716
Other long-term liabilities	1,023	3,660
Total liabilities	548,755	472,050
Stockholders’ equity:
Preferred stock, $0.01 par value per share; 10,000,000 shares authorized at June 30, 2019 and December 31, 2018; 0 shares issued at June 30, 2019 and December 31, 2018	0	0
Common stock, $0.01 par value per share; 100,000,000 shares authorized at June 30, 2019 and December 31, 2018; 49,284,448 and 48,087,257 shares issued at June 30, 2019 and December 31, 2018, respectively; 48,797,640 and 47,600,449 shares outstanding at June 30, 2019 and December 31, 2018, respectively	488	476
Treasury stock, at cost, 486,808 shares at June 30, 2019 and December 31, 2018	(4,764)	(4,764)
Additional paid-in-capital	581,127	556,223
Accumulated other comprehensive income (loss)	351	(31)
Accumulated deficit	(489,678)	(464,585)
Total stockholders’ equity	87,524	87,319
Total liabilities and stockholders’ equity	$ 636,279	$ 559,369