Condensed Consolidated Statements of Stockholders’ Equity (Deficit) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Restricted Stock Units Common Stock	Restricted Stock Common Stock
Beginning balance (in shares) at Jan. 31, 2018		220,979
Beginning balance at Jan. 31, 2018	$ 574,401	$ 22	$ 1,479,883	$ (1,917)	$ (903,587)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		2,194
Issuance of common stock upon exercise of stock options	9,630	$ 0	9,630
Stock-based compensation expense	43,955		43,955
Vesting of early exercised stock options	320		320
Vesting of restricted stock units (in shares)						2,013
Vesting of restricted stock units	0	$ 0	0
Common stock issued under employee stock purchase plan (in shares)		2,110
Common stock issued under employee stock purchase plan	19,698		19,698
Issuance of restricted stock awards (in shares)							3,309
Issuance of restricted stock	1						$ 1
Repurchase of Common Stock (in shares)		(1,009)
Repurchase of common stock	(20,000)		(20,000)
Purchase of capped calls	(64,630)		(64,630)
Equity component of convertible senior notes, net	133,265		133,265
Other comprehensive loss	(716)			(716)
Net loss	(64,304)				(64,304)
Ending balance (in shares) at Apr. 30, 2018		229,596
Ending balance at Apr. 30, 2018	631,620	$ 23	1,602,121	(2,633)	(967,891)
Beginning balance (in shares) at Jan. 31, 2019		243,524
Beginning balance at Jan. 31, 2019	737,780	$ 24	1,820,043	(338)	(1,081,949)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		3,208
Issuance of common stock upon exercise of stock options	16,789	$ 1	16,788
Stock-based compensation expense	61,746		61,746
Vesting of restricted stock units (in shares)						2,050
Vesting of restricted stock units	0		0
Tax withholding on vesting of restricted stock	(5,672)		(5,672)
Common stock issued under employee stock purchase plan (in shares)		2,973
Common stock issued under employee stock purchase plan	32,042		32,042
Issuance of restricted stock awards (in shares)							1,098
Issuance of restricted stock	0
Other comprehensive loss	1,627			1,627
Net loss	(100,336)				(100,336)
Ending balance (in shares) at Apr. 30, 2019		252,853
Ending balance at Apr. 30, 2019	$ 743,976	$ 25	$ 1,924,947	$ 1,289	$ (1,182,285)