Summary of Significant Accounting Policies - Property and Equipment, Net (Details) - USD ($)	3 Months Ended			6 Months Ended
	Jul. 31, 2019	Apr. 30, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018	Jan. 31, 2019
Capitalized Internal Use Software
Impairments of internal use software	$ 0		$ 0
Capitalized amount of internal use software	1,500,000			$ 3,500,000	$ 3,200,000
Amortization expense associated with internal use software	1,600,000		1,200,000	3,000,000.0	2,300,000
Net book value of capitalized internal use software	12,000,000.0			12,000,000.0		$ 11,500,000
Deferred Contract Acquisition Costs
Contract acquisition cost amortization expense	7,700,000		6,400,000	$ 15,100,000	12,000,000.0
Amortization over an estimated period of benefit for commissions, including referral fees paid to channel partner				4 years
Amortization over an estimated period of benefit for sales commissions associated with professional service contract				6 months
Capitalization of contract acquisition costs	19,317,000	$ 19,300,000	9,272,000	$ 27,788,000	14,298,000
Impairment of Long Lived Assets
Impairment losses of long lived assets	$ 0		$ 0	$ 0	$ 0
Minimum
Intangible Assets, Net
Estimated economic lives				3 years
Maximum
Intangible Assets, Net
Estimated economic lives				5 years
Data center and other computer equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives				3 years
Data center and other computer equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives				5 years
Furniture and equipment
Property, Plant and Equipment [Line Items]
Estimated useful lives				5 years
Purchased software | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives				3 years
Purchased software | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives				5 years
Capitalized internal-use software
Property, Plant and Equipment [Line Items]
Estimated useful lives				3 years