Recast Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	$ 67,052	$ 53,365	$ 182,770	$ 142,389
Cost of revenues	7,052	5,423	19,934	14,997
Gross profit	60,000	47,942	162,836	127,392
Research and development	17,267	11,903	50,526	33,810
Sales and marketing	40,792	32,458	122,113	95,952
General and administrative	8,774	6,708	23,832	18,796
Total operating expenses	66,833	51,069	196,471	148,558
Operating loss	(6,833)	(3,127)	(33,635)	(21,166)
Financial income (expenses), net	99	622	266	2,041
Loss before income taxes	(6,734)	(2,505)	(33,369)	(19,125)
Income taxes	(583)	(759)	(1,677)	(1,539)
Net loss	(7,317)	(3,264)	(35,046)	(20,664)
Prepaid expenses and other current assets	14,665		14,665		$ 14,346
Other assets	7,601		7,601		7,243
Deferred revenues	72,544		72,544		73,493
Deferred revenues	6,374		6,374		6,608
Other liabilities	7,651		7,651		7,807
Accumulated deficit	(144,436)		(144,436)		(109,390)
Amortization of deferred commissions			9,718	9,292
Deferred commissions			(9,864)	(9,511)
Deferred revenues			(1,183)	3,161
Other long term liabilities			(155)	(421)
Net cash provided by operating activities			16,265	10,846
As Reported
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue		53,601		144,155
Cost of revenues		5,436		14,986
Gross profit		48,165		129,169
Research and development		11,903		33,810
Sales and marketing		32,802		96,173
General and administrative		6,711		18,806
Total operating expenses		51,416		148,789
Operating loss		(3,251)		(19,620)
Financial income (expenses), net		622		2,041
Loss before income taxes		(2,629)		(17,579)
Income taxes		(685)		(1,649)
Net loss		(3,314)		(19,228)
Prepaid expenses and other current assets					7,130
Other assets					973
Deferred revenues					73,891
Deferred revenues					7,034
Other liabilities					6,561
Accumulated deficit					(122,454)
Amortization of deferred commissions				0
Deferred commissions				0
Deferred revenues				1,390
Other long term liabilities				(305)
Net cash provided by operating activities				10,846
Adjustments | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue		(236)		(1,766)	(1,974)
Cost of revenues		(13)		11
Gross profit		(223)		(1,777)
Research and development		0		0
Sales and marketing		(344)		(221)
General and administrative		(3)		(10)
Total operating expenses		(347)		(231)
Operating loss		124		(1,546)
Financial income (expenses), net		0		0
Loss before income taxes		124		(1,546)
Income taxes		(74)		110
Net loss		50		(1,436)
Prepaid expenses and other current assets					7,216
Other assets					6,270
Deferred revenues					(398)
Deferred revenues					(426)
Other liabilities					1,246
Accumulated deficit					$ 13,064
Amortization of deferred commissions				9,292
Deferred commissions				(9,511)
Deferred revenues				1,771
Other long term liabilities				(116)
Net cash provided by operating activities				0
Licenses
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	35,804	29,000	94,338	74,402
Licenses | As Reported
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue		29,409		76,984
Licenses | Adjustments | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue		(409)		(2,582)
Maintenance and services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	$ 31,248	24,365	$ 88,432	67,987
Maintenance and services | As Reported
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue		24,192		67,171
Maintenance and services | Adjustments | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue		$ 173		$ 816