Consolidated Statements Stockholders' Equity - USD ($) $ in Thousands		Total	Class A & B Common Stock	Additional Paid-in Capital	Retained Earnings	AOCI Attributable to Parent
Beginning balance at Jan. 31, 2017		$ 678,154	$ 1	$ 439,658	$ 238,384	$ 111
Beginning balance (in shares) at Jan. 31, 2017			137,886,619
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options		21,194		21,194
Issuance of common stock upon exercise of stock options (in shares)			2,935,962
Vesting of early exercised stock options		1		1
Issuance of common stock upon vesting of restricted stock units (in shares)			1,246,815
Stock-based compensation expense		54,419		54,419
Other comprehensive income (loss)		1,293			(196)	1,489
Net income		151,177			151,177
Ending balance at Jan. 31, 2018		906,238	$ 1	515,272	389,365	1,600
Ending 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		25,554		25,554
Issuance of common stock upon exercise of stock options (in shares)			2,807,092
Issuance of common stock upon vesting of restricted stock units (in shares)			1,313,591
Stock-based compensation expense		76,797		76,797
Other comprehensive income (loss)		(672)				(672)
Net income		229,832			229,832
Ending balance at Jan. 31, 2019		1,237,749	$ 1	617,623	619,197	928
Ending 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		$ 10,899		10,899
Issuance of common stock upon exercise of stock options (in shares)		1,665,778	1,665,778
Issuance of common stock upon vesting of restricted stock units (in shares)			1,239,726
Stock-based compensation expense		$ 116,296		116,296
Other comprehensive income (loss)		(468)				(468)
Net income		301,118			301,118
Replacement award value in connection with business combination		657		657
Ending balance at Jan. 31, 2020		1,665,594	$ 1	$ 745,475	919,658	$ 460
Ending balance (in shares) at Jan. 31, 2020			149,095,583
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment for Topic 842	[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.