Summary of Significant Accounting Policies - Narrative (Details)					12 Months Ended
	Feb. 01, 2019 USD ($)	Sep. 18, 2018 USD ($) $ / shares shares	May 01, 2018 USD ($) $ / shares shares	Apr. 26, 2018	Jan. 31, 2020 USD ($) segment reporting_unit shares	Jan. 31, 2019 USD ($) shares	Jan. 31, 2018 USD ($)	Mar. 31, 2019 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from issuance initial public offering			$ 523,900,000		$ 0	$ 529,305,000	$ 0
Underwriting discounts and commissions			30,800,000
Other offering expenses			$ 5,400,000
Redeemable convertible preferred stock, shares issued (in shares) | shares			100,200,000
Warrant liability reclassified into additional paid in capital					$ 800,000	$ 848,000
Common stock, shares authorized (in shares) | shares			500,000,000.0		500,000,000	500,000,000
Preferred stock, shares authorized (in shares) | shares			10,000,000.0		10,000,000	10,000,000
Stock issuance costs					$ 0	$ 4,011,000	315,000
Advertising expense					41,600,000	34,100,000	19,300,000
Foreign currency transaction gain (loss)					(1,000,000.0)	(3,400,000)	2,200,000
Equity investments in privately held companies						0		$ 15,500,000
Allowance for doubtful accounts					(3,000,000.0)	(600,000)
Unbilled accounts receivable					1,600,000	1,500,000
Impairment of goodwill					$ 0	0	0
Number of operating segments | segment					1
Number of reporting units | reporting_unit					1
Number of reportable segments | segment					1
Right of use asset					$ 149,833,000	0
Lease liability					183,160,000
Derecognition of build-to-suit lease					2,479,000	$ 0	$ 0
Convertible Debt | Convertible Senior Notes Due 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate principal amount of debt issued					$ 575,000,000.0
Debt interest rate percentage					0.50%
Convertible Debt | Convertible Senior Notes Due 2023 | Measurement Input, Discount Rate
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount rate					0.06
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
ESPP offering period				6 months
IPO
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued and sold, IPO (in shares) | shares			19,300,000
Price per share, IPO (in usd per share) | $ / shares			$ 29.00
Over-Allotment Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued and sold, IPO (in shares) | shares			3,300,000
IPO - Shares From Existing Shareholders
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued and sold, IPO (in shares) | shares			5,600,000
Follow-On Offering
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued and sold, IPO (in shares) | shares		8,100,000
Price per share, IPO (in usd per share) | $ / shares		$ 55.00
Stock issuance costs		$ 1,300,000
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued upon conversion (in shares) | shares			100,400,000			100,350,000
Exercise of common stock warrants (in shares) | shares						22,000
Accounting Standards Update 2016-02
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Derecognition of deferred rent	$ 26,600,000
Right of use asset	93,900,000
Lease liability	121,800,000
Derecognition of build-to-suit lease	$ 2,500,000
Initial Acquisition Of Contract
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Commissions paid, amortization period					5 years
Renewal Contracts
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Commissions paid, amortization period					2 years
Software, including capitalized software development costs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected useful life					3 years
Customer Concentration Risk | One Customer | Accounts Receivable
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Concentration risk percentage					9.00%	10.00%