Equity Incentive Plans - Additional Information (Details)			1 Months Ended		3 Months Ended	12 Months Ended				84 Months Ended
	Mar. 16, 2016 USD ($)	Jul. 31, 2014 USD ($) shares	Nov. 30, 2016 shares	Aug. 31, 2015 USD ($) period shares	Jan. 31, 2017 USD ($) $ / shares shares	Jan. 31, 2017 USD ($) plan $ / shares shares	Jan. 31, 2016 USD ($) $ / shares shares	Jan. 31, 2015 USD ($) $ / shares shares	Jan. 31, 2014 USD ($) shares	Jan. 31, 2015 USD ($)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of equity incentive plans | plan						2
Shares reserved for future equity awards (in shares) | shares					93,048,923	93,048,923
Stock-based compensation expense						$ 116,668,000	$ 58,225,000	$ 53,033,000
Unrecognized compensation cost related to stock awards, weighted-average period						2 years 10 months 24 days
Issuance of common stock upon exercise of stock options (in shares) | shares						10,180,258
Unrecognized compensation cost					$ 132,600,000	$ 132,600,000
Shares underlying outstanding equity awards (in shares) | shares					56,840,189	56,840,189	68,879,087
Number of options granted (in shares) | shares						1,999,000
Fair value on the respective vesting dates					$ 228,436,000	$ 228,436,000
Payment for repurchase of common stock and vested stock options		$ 57,700,000
Tender Offer
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Proceeds from stock options exercised		$ 2,100,000
Repurchase Of Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense								$ 27,600,000
Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested stock option, common stock repurchased during the period (in shares) | shares								3,803,000
Repurchase of shares (in shares) | shares		735,426
Accumulated Deficit
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Repurchase of recorded in accumulated deficit		$ 30,100,000
Promissory Notes
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of common stock upon exercise of stock options (in shares) | shares								300,000	6,295,056
Notes payable									$ 3,200,000
Value of options exercised								$ 773,000		$ 4,000,000
Equity awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved for future equity awards (in shares) | shares					24,457,623	24,457,623
Intrinsic value of exercised options						$ 114,200,000	$ 29,500,000	$ 43,200,000
Weighted-average grant date fair value of options granted (in dollars per share) | $ / shares						$ 5.57	$ 8.38	$ 5.71
Total grant date fair value of options vested						$ 61,800,000	$ 35,400,000	$ 9,900,000
Plan modification, number of shares affected (in shares) | shares			800,000
Plan modification, incremental compensation cost					$ 5,900,000
Dividend rate						0.00%	0.00%	0.00%
Repurchase of shares (in shares) | shares		3,067,910
Equity awards | Early Exercise of Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of common stock upon exercise of stock options (in shares) | shares						0	642,248
Proceeds from stock options exercised							$ 1,900,000
Unvested stock option, common stock repurchased during the period (in shares) | shares						0	15,000	50,000
Common stock subject to repurchase (in shares) | shares					494,117	494,117	2,809,264
Common stock subject to repurchase, aggregate price					$ 1,400,000.0	$ 1,400,000.0	$ 4,800,000.0
Performance Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense						$ 3,300,000	$ 2,500,000	$ 1,700,000
Number of options granted, net of cancellations (in shares) | shares							238,000	499,750
Shares underlying outstanding equity awards (in shares) | shares					0	0
Plan modification, number of shares affected (in shares) | shares			360,000
Restricted stock units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved for future equity awards (in shares) | shares					8,783,024	8,783,024
Unrecognized compensation cost related to stock awards, weighted-average period						2 years 10 months
Plan modification, number of shares affected (in shares) | shares			440,000
Vested in period, fair value						$ 14,800,000
Unrecognized employee compensation cost					$ 103,100,000	$ 103,100,000
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Dividend rate						0.00%	0.00%	0.00%
Non Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense						$ 700,000	$ 3,100,000	$ 2,500,000
Number of options granted (in shares) | shares						0	22,500	83,500
Minimum | Promissory Notes
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Debt instrument, interest rate					0.95%	0.95%
Maximum | Promissory Notes
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Debt instrument, interest rate					1.84%	1.84%
2015 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Equity awards of vest expire period						10 years
2015 Equity Incentive Plan | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase price as percentage of fair market value of common stock						100.00%
Equity awards of vest period						2 years
2015 Equity Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Equity awards of vest period						4 years
2015 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Employee stock purchase plan offering period	24 months
Number of purchase periods | period				4
Purchase period, term				6 months
E S P P modification charge	$ 10,600,000
Stock-based compensation expense						$ 18,300,000	$ 4,400,000
Unrecognized stock-based compensation expense					$ 22,100,000	$ 22,100,000
Unrecognized compensation cost related to stock awards, weighted-average period						1 year 67 days
Stock-based Compensation Expense Related to Tender Offer
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense		$ 27,600,000
Class A common stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Closing price of stock (in dollars per share) | $ / shares					$ 11.37	$ 11.37
Class A common stock | 2015 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares initially reserved for issuance (in shares) | shares					27,000,000	27,000,000
Increase in shares reserved by percentage of capital stock						5.00%
Class A common stock | 2015 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in shares reserved by percentage of capital stock				1.00%
Purchase price as percentage of fair market value of common stock				85.00%
Shares reserved for future equity awards (in shares) | shares				3,500,000
Payroll deductions percentage				30.00%
Share cap for ESPP at purchase date (in shares) | shares				3,000
Calendar year gap for ESPP contribution amount				$ 25,000