Commitments and Contingencies - Narrative (Details)	1 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($) renewal_option	Jan. 31, 2018 USD ($)	Jan. 31, 2017 USD ($)	Jan. 31, 2016 USD ($)	Aug. 31, 2017 USD ($)
Other Commitments [Line Items]
Lease commitment amount		$ 254,461,000
Restricted cash		8,284,000	$ 0	$ 3,673,000
Deferred rent		5,500,000	4,800,000
Rent expense		10,600,000	7,400,000	$ 5,200,000
Letter of Credit
Other Commitments [Line Items]
Letters of credit issued and outstanding		12,200,000	5,400,000
Draws on letters of credit		$ 0
San Francisco - 9 Year Lease
Other Commitments [Line Items]
Lease term		9 years
Proceeds received for tenant incentives			$ 1,800,000
Number of renewal options | renewal_option	2
Lease renewal term	5 years
San Francisco - 10 Year Lease
Other Commitments [Line Items]
Lease term	10 years
Lease commitment amount	$ 206,300,000
Tenant improvement allowance (up to)	$ 24,700,000.0
Restricted cash		$ 8,000,000
San Jose Office Space, Amendment
Other Commitments [Line Items]
Lease commitment amount					$ 6,600,000
Tenant improvement allowance (up to)					$ 800,000.0