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)		5,884
Issuance of common stock upon exercise of stock options	29,066	$ 1	29,065
Stock-based compensation expense	97,609		97,609
Vesting of restricted stock units (in shares)						4,117
Vesting of restricted stock units	0	$ 0	0
Vesting of early exercised stock options	320		320
Common stock issued under employee stock purchase plan (in shares)		2,111
Common stock issued under employee stock purchase plan	19,698		19,698
Issuance of restricted stock awards (in shares)							3,330
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	(909)			(909)
Net loss	(124,427)				(124,427)
Ending balance (in shares) at Jul. 31, 2018		235,412
Ending balance at Jul. 31, 2018	644,394	$ 24	1,675,210	(2,826)	(1,028,014)
Beginning balance (in shares) at Apr. 30, 2018		229,596
Beginning balance at Apr. 30, 2018	631,620	$ 23	1,602,121	(2,633)	(967,891)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		3,691
Issuance of common stock upon exercise of stock options	19,436	$ 1	19,435
Stock-based compensation expense	53,654		53,654
Vesting of restricted stock units (in shares)						2,104
Vesting of restricted stock units	0	$ 0	0
Issuance of restricted stock awards (in shares)							21
Issuance of restricted stock	0						$ 0
Other comprehensive loss	(193)			(193)
Net loss	(60,123)				(60,123)
Ending balance (in shares) at Jul. 31, 2018		235,412
Ending balance at Jul. 31, 2018	644,394	$ 24	1,675,210	(2,826)	(1,028,014)
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)		3,863
Issuance of common stock upon exercise of stock options	19,291	$ 1	19,290
Stock-based compensation expense	118,206		118,206
Vesting of restricted stock units (in shares)						4,327
Vesting of restricted stock units	0	$ 1	(1)
Tax withholding on vesting of restricted stock	(7,173)		(7,173)
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)							1,065
Other comprehensive loss	3,747			3,747
Net loss	(166,354)				(166,354)
Ending balance (in shares) at Jul. 31, 2019		255,752
Ending balance at Jul. 31, 2019	737,539	$ 26	1,982,407	3,409	(1,248,303)
Beginning balance (in shares) at Apr. 30, 2019		252,853
Beginning balance at Apr. 30, 2019	743,976	$ 25	1,924,947	1,289	(1,182,285)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		655
Issuance of common stock upon exercise of stock options	2,502	$ 0	2,502
Stock-based compensation expense	56,460		56,460
Vesting of restricted stock units (in shares)						2,277
Vesting of restricted stock units	0	$ 1	(1)
Tax withholding on vesting of restricted stock	(1,501)		(1,501)
Issuance of restricted stock awards (in shares)							(33)
Issuance of restricted stock	0
Other comprehensive loss	2,120			2,120
Net loss	(66,018)				(66,018)
Ending balance (in shares) at Jul. 31, 2019		255,752
Ending balance at Jul. 31, 2019	$ 737,539	$ 26	$ 1,982,407	$ 3,409	$ (1,248,303)