Consolidated Statements of Convertible Preferred Stock and Stockholders’ Equity (Deficit) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Series E Convertible Preferred Stock	Series F Convertible Preferred Stock	Series F-1 Convertible Preferred Stock
Beginning balance (in shares) at Jan. 31, 2014	104,106
Beginning balance at Jan. 31, 2014	$ 262,970
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of convertible preferred stock (in shares)						65	14,308	3,802
Issuance of convertible preferred stock						$ 450	$ 220,803	$ 59,717
Ending balance (in shares) at Jan. 31, 2015	122,281
Ending balance at Jan. 31, 2015	$ 543,940
Beginning balance (in shares) at Jan. 31, 2014		28,439
Beginning balance at Jan. 31, 2014	(116,087)	$ 3	$ 12,143	$ 0	$ (128,233)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options, including stock options exercised via promissory notes (Note 7) (in shares)		11,879
Issuance of common stock upon exercise of stock options, including stock options exercised via promissory notes (Note 7)	3,047	$ 2	3,045
Repurchase of common stock in connection with tender offer (Note 7) (in shares)		(3,803)
Repurchase of common stock in connection with tender offer (Note 7)	(30,120)	$ (1)			(30,119)
Repurchase of common stock from early exercised stock options (in shares)		(50)
Repurchase of common stock from early exercised stock options	0
Stock-based compensation expense	25,399		25,399
Vesting of early exercised stock options	1,162		1,162
Net loss	(183,231)				(183,231)
Ending balance (in shares) at Jan. 31, 2015		36,465
Ending balance at Jan. 31, 2015	$ (299,830)	$ 4	41,749	0	(341,583)
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of convertible preferred stock to common stock upon initial public offering (in shares)	(122,281)
Conversion of convertible preferred stock to common stock upon initial public offering	$ (543,940)
Ending balance (in shares) at Jan. 31, 2016	0
Ending balance at Jan. 31, 2016	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of convertible preferred stock to common stock upon initial public offering (in shares)		122,281
Conversion of convertible preferred stock to common stock upon initial public offering	543,940	$ 12	543,928
Issuance of common stock upon initial public offering (in shares)		28,750
Issuance of common stock upon initial public offering, net of offering costs	455,138	$ 3	455,135
Issuance of common stock to Pure Good Foundation (in shares)		700
Issuance of common stock to Pure Good Foundation	11,900		11,900
Issuance of common stock upon exercise of stock options, net of repurchases (in shares)		2,313
Issuance of common stock upon exercise of stock options, net of repurchases	6,008	$ 0	6,008
Stock-based compensation expense	58,225		58,225
Vesting of early exercised stock options	1,725		1,725
Net loss	(213,752)				(213,752)
Ending balance (in shares) at Jan. 31, 2016		190,509
Ending balance at Jan. 31, 2016	$ 563,354	$ 19	1,118,670	0	(555,335)
Ending balance (in shares) at Jan. 31, 2017	0
Ending balance at Jan. 31, 2017	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment from adoption of ASU 2016-09 | Accounting Standards Update 2016-09	0		2,079		(2,079)
Issuance of common stock upon exercise of stock options, net of repurchases (in shares)		10,180
Issuance of common stock upon exercise of stock options, net of repurchases	15,031	$ 1	15,030
Stock-based compensation expense	116,668		116,668
Vesting of early exercised stock options	3,399		3,399
Vesting of restricted stock units (in shares)		1,238
Vesting of restricted stock units	0
Common stock issued under employee stock purchase plan (in shares)		2,437
Common stock issued under employee stock purchase plan	25,606		25,606
Other comprehensive income (loss)	(562)			(562)
Net loss	(245,066)				(245,066)
Ending balance (in shares) at Jan. 31, 2017		204,364
Ending balance at Jan. 31, 2017	$ 478,430	$ 20	$ 1,281,452	$ (562)	$ (802,480)