Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands		Total	Class A & B common stock	Additional paid-in capital	Retained earnings	Accumulated other comprehensive income
Beginning balance at Jan. 31, 2018		$ 906,238	$ 1	$ 515,272	$ 389,365	$ 1,600
Beginning balance (in shares) at Jan. 31, 2018			142,069,396
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options		19,293		19,293
Issuance of common stock upon exercise of stock options (in shares)			2,012,604
Issuance of common stock upon vesting of restricted stock units (in shares)			986,417
Stock-based compensation expense		56,932		56,932
Other comprehensive income		(2,839)				(2,839)
Net income		158,681			158,681
Ending balance at Oct. 31, 2018		1,138,305	$ 1	591,497	548,046	(1,239)
Ending balance (in shares) at Oct. 31, 2018			145,068,417
Beginning balance at Jul. 31, 2018		1,050,376	$ 1	566,533	483,961	(119)
Beginning balance (in shares) at Jul. 31, 2018			144,144,488
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options		4,923		4,923
Issuance of common stock upon exercise of stock options (in shares)			599,655
Issuance of common stock upon vesting of restricted stock units (in shares)			324,274
Stock-based compensation expense		20,041		20,041
Other comprehensive income		(1,120)				(1,120)
Net income		64,085			64,085
Ending balance at Oct. 31, 2018		1,138,305	$ 1	591,497	548,046	(1,239)
Ending balance (in shares) at Oct. 31, 2018			145,068,417
Beginning balance at Jan. 31, 2019		1,237,749	$ 1	617,623	619,197	928
Beginning balance (in shares) at Jan. 31, 2019			146,190,079
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options		$ 8,503		8,503
Issuance of common stock upon exercise of stock options (in shares)		1,225,746	1,225,746
Issuance of common stock upon vesting of restricted stock units (in shares)			944,996
Stock-based compensation expense		$ 78,789		78,789
Other comprehensive income		(755)				(755)
Net income		234,936			234,936
Ending balance at Oct. 31, 2019		1,558,565	$ 1	704,915	853,476	173
Ending balance (in shares) at Oct. 31, 2019			148,360,821
Beginning balance at Jul. 31, 2019		1,445,017	$ 1	673,878	771,231	(93)
Beginning balance (in shares) at Jul. 31, 2019			147,848,634
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options		1,588		1,588
Issuance of common stock upon exercise of stock options (in shares)			211,154
Issuance of common stock upon vesting of restricted stock units (in shares)			301,033
Stock-based compensation expense		29,449		29,449
Other comprehensive income		266				266
Net income		82,245			82,245
Ending balance at Oct. 31, 2019		1,558,565	$ 1	$ 704,915	853,476	$ 173
Ending balance (in shares) at Oct. 31, 2019			148,360,821
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment for Topic 842 adoption	[1]	$ (657)			$ (657)

[1] We adopted ASU 2016-02, “Leases” (Topic 842) using the modified retrospective method as of February 1, 2019 and elected the transition option that allows us not to restate the comparative periods in our financial statements in the year of adoption.