Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Class A & B common stock	Additional paid-in capital	Retained earnings	Retained earnings Cumulative Effect, Period of Adoption, Adjustment	Accumulated other comprehensive income
Beginning balance (in shares) at Jan. 31, 2019			146,190,079
Beginning balance at Jan. 31, 2019	$ 1,237,749	$ (657)	$ 1	$ 617,623	$ 619,197	$ (657)	$ 928
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)			1,225,746
Issuance of common stock upon exercise of stock options	8,503			8,503
Issuance of common stock upon vesting of restricted stock units (in shares)			944,996
Issuance of common stock upon vesting of restricted stock units	0
Stock-based compensation expense	78,789			78,789
Other comprehensive income	(755)						(755)
Net income	234,936				234,936
Ending balance (in shares) at Oct. 31, 2019			148,360,821
Ending balance at Oct. 31, 2019	1,558,565		$ 1	704,915	853,476		173
Beginning balance (in shares) at Jul. 31, 2019			147,848,634
Beginning balance at Jul. 31, 2019	1,445,017		$ 1	673,878	771,231		(93)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)			211,154
Issuance of common stock upon exercise of stock options	1,588			1,588
Issuance of common stock upon vesting of restricted stock units (in shares)			301,033
Issuance of common stock upon vesting of restricted stock units	0
Stock-based compensation expense	29,449			29,449
Other comprehensive income	266						266
Net income	82,245				82,245
Ending balance (in shares) at Oct. 31, 2019			148,360,821
Ending balance at Oct. 31, 2019	1,558,565		$ 1	704,915	853,476		173
Beginning balance (in shares) at Jan. 31, 2020			149,095,583
Beginning balance at Jan. 31, 2020	$ 1,665,594		$ 1	745,475	919,658		460
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)	1,407,370		1,407,370
Issuance of common stock upon exercise of stock options	$ 25,209		$ 1	25,208
Issuance of common stock upon vesting of restricted stock units (in shares)			780,575
Issuance of common stock upon vesting of restricted stock units	0
Stock-based compensation expense	135,454			135,454
Other comprehensive income	3,042						3,042
Net income	277,080				277,080
Ending balance (in shares) at Oct. 31, 2020			151,283,528
Ending balance at Oct. 31, 2020	2,106,379		$ 2	906,137	1,196,738		3,502
Beginning balance (in shares) at Jul. 31, 2020			150,739,850
Beginning balance at Jul. 31, 2020	1,956,727		$ 2	850,776	1,099,779		6,170
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)			300,999
Issuance of common stock upon exercise of stock options	6,180			6,180
Issuance of common stock upon vesting of restricted stock units (in shares)			242,679
Issuance of common stock upon vesting of restricted stock units	0
Stock-based compensation expense	49,181			49,181
Other comprehensive income	(2,668)						(2,668)
Net income	96,959				96,959
Ending balance (in shares) at Oct. 31, 2020			151,283,528
Ending balance at Oct. 31, 2020	$ 2,106,379		$ 2	$ 906,137	$ 1,196,738		$ 3,502