New Accounting Pronouncements - Select Unaudited Condensed Consolidated Balance Sheet Line Items (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Assets:
Deferred commissions, current portion	$ 10,093	$ 9,551
Deferred commissions, net of current portion	21,825	20,404
Liabilities, redeemable convertible and convertible preferred stock and stockholders' equity (deficit):
Deferred revenue, current portion	129,927	130,165
Deferred revenue, net of current portion	39,344	38,535
Accumulated deficit	$ (501,330)	(273,513)
Calculated under Revenue Guidance in Effect before Topic 606 | Accounting Standards Update 2014-09
Assets:
Deferred commissions, current portion		15,195
Deferred commissions, net of current portion		3,811
Liabilities, redeemable convertible and convertible preferred stock and stockholders' equity (deficit):
Deferred revenue, current portion		132,278
Deferred revenue, net of current portion		31,902
Accumulated deficit		(279,942)
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Assets:
Deferred commissions, current portion		(5,644)
Deferred commissions, net of current portion		16,593
Liabilities, redeemable convertible and convertible preferred stock and stockholders' equity (deficit):
Deferred revenue, current portion		(2,113)
Deferred revenue, net of current portion		6,633
Accumulated deficit		$ 6,429