Condensed Consolidated Statements of Stockholders’ Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Restricted Stock Units	Restricted Stock Units Common Stock	Restricted Stock Units Additional Paid-In Capital	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)		8,250
Issuance of common stock upon exercise of stock options	43,378	$ 1	43,377
Stock-based compensation expense	155,938		155,938
Vesting of early exercised stock options	320		320
Vesting of restricted stock units (in shares)							6,429
Common stock issued under employee stock purchase plan (in shares)		3,380
Common stock issued under employee stock purchase plan	33,444		33,444
Net issuance of restricted stock (in shares)									3,330
Net 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 income (loss)	(1,182)			(1,182)
Net loss	(152,607)				(152,607)
Ending balance (in shares) at Oct. 31, 2018		241,359
Ending balance at Oct. 31, 2018	702,328	$ 24	1,761,597	(3,099)	(1,056,194)
Beginning balance (in shares) at Jul. 31, 2018		235,412
Beginning balance at Jul. 31, 2018	644,394	$ 24	1,675,210	(2,826)	(1,028,014)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		2,366
Issuance of common stock upon exercise of stock options	14,312		14,312
Stock-based compensation expense	58,329		58,329
Vesting of restricted stock units (in shares)							2,312
Common stock issued under employee stock purchase plan (in shares)		1,269
Common stock issued under employee stock purchase plan	13,746		13,746
Other comprehensive income (loss)	(273)			(273)
Net loss	(28,180)				(28,180)
Ending balance (in shares) at Oct. 31, 2018		241,359
Ending balance at Oct. 31, 2018	702,328	$ 24	1,761,597	(3,099)	(1,056,194)
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)		4,797
Issuance of common stock upon exercise of stock options	26,006	$ 1	26,005
Stock-based compensation expense	170,542		170,542
Vesting of restricted stock units (in shares)							6,884
Vesting of restricted stock units						$ 0	$ 1	$ (1)
Common stock issued under employee stock purchase plan (in shares)		3,743
Common stock issued under employee stock purchase plan	43,291		43,291
Net issuance of restricted stock (in shares)									972
Tax withholding on vesting of restricted stock	(8,787)		(8,787)
Other comprehensive income (loss)	5,454			5,454
Net loss	(196,336)				(196,336)
Ending balance (in shares) at Oct. 31, 2019		259,920
Ending balance at Oct. 31, 2019	777,950	$ 26	2,051,093	5,116	(1,278,285)
Beginning balance (in shares) at Jul. 31, 2019		255,752
Beginning balance at Jul. 31, 2019	737,539	$ 26	1,982,407	3,409	(1,248,303)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		934
Issuance of common stock upon exercise of stock options	6,715		6,715
Stock-based compensation expense	52,336		52,336
Vesting of restricted stock units (in shares)							2,557
Common stock issued under employee stock purchase plan (in shares)		770
Common stock issued under employee stock purchase plan	11,249		11,249
Net issuance of restricted stock (in shares)									(93)
Tax withholding on vesting of restricted stock	(1,614)		(1,614)
Other comprehensive income (loss)	1,707			1,707
Net loss	(29,982)				(29,982)
Ending balance (in shares) at Oct. 31, 2019		259,920
Ending balance at Oct. 31, 2019	$ 777,950	$ 26	$ 2,051,093	$ 5,116	$ (1,278,285)