Summary of Significant Accounting Policies - Narrative (Details) - USD ($)	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Payment terms for deferred revenue	30 days
Payment terms for deferred commissions	3 months
Advertising expenses	$ 9,400,000	$ 4,400,000	$ 3,700,000
Deferred offering costs	0	3,700,000
Cumulative impact adjustment		0
Goodwill impairments	$ 0	0	$ 0
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative impact adjustment		200,000
Retained Earnings | Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative impact adjustment		$ 200,000
ESPP
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Expected dividend yield	0.00%
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue recognition, customer contract period	1 year
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue recognition, customer contract period	3 years
Capitalized internal-use software costs
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Intangible asset, useful life	3 years
Pro Forma | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred incremental commission costs, amortization period	5 years