Summary of Significant Accounting Policies - Narrative (Details)	12 Months Ended
	Jan. 31, 2019 USD ($) segment	Jan. 31, 2018 USD ($)	Jan. 31, 2017 USD ($)	May 01, 2018 USD ($)
Lessee, Lease, Description [Line Items]
Number of operating segments | segment	1
Interest income	$ 3,300,000	$ 500,000	$ 400,000
Internal use software costs capitalized	3,500,000	3,400,000
Costs incurred during development for platform to sell subscriptions	1,500,000	0
Amortization expense of capitalized internal-use software costs	1,000,000	200,000	0
Deferred rent	2,000,000	600,000
Net self insurance reserve estimate	800,000	600,000
Advertising and marketing expenses	20,600,000	14,800,000	10,500,000
Deferred offering costs capitalized				$ 3,400,000
Investing activity increase	(13,784,000)	(809,000)	9,641,000
Bellevue, Boston, London and Edinburgh Leases
Lessee, Lease, Description [Line Items]
Security deposits	800,000
Bellevue and Boston Leases
Lessee, Lease, Description [Line Items]
Security deposits		500,000
Boston Lease
Lessee, Lease, Description [Line Items]
Security deposits			300,000
Financial Standby Letter of Credit | Bellevue Lease
Lessee, Lease, Description [Line Items]
Irrevocable letters of credit	$ 1,800,000
Financial Standby Letter of Credit | Bellevue and Boston Leases
Lessee, Lease, Description [Line Items]
Irrevocable letters of credit		2,400,000	1,600,000
Accounting Standards Update 2016-18
Lessee, Lease, Description [Line Items]
Investing activity increase		$ 1,000,000	$ 600,000
Software
Lessee, Lease, Description [Line Items]
Software useful life	3 years