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		14,370		14,370
Issuance of common stock upon exercise of stock options (in shares)			1,412,949
Issuance of common stock upon vesting of restricted stock units (in shares)			662,143
Stock-based compensation expense		36,891		36,891
Other comprehensive income		(1,719)				(1,719)
Net income		94,596			94,596
Ending balance at Jul. 31, 2018		1,050,376	$ 1	566,533	483,961	(119)
Ending balance (in shares) at Jul. 31, 2018			144,144,488
Beginning balance at Apr. 30, 2018		974,437	$ 1	539,665	433,675	1,096
Beginning balance (in shares) at Apr. 30, 2018			143,176,585
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options		7,041		7,041
Issuance of common stock upon exercise of stock options (in shares)			624,571
Issuance of common stock upon vesting of restricted stock units (in shares)			343,332
Stock-based compensation expense		19,827		19,827
Other comprehensive income		(1,215)				(1,215)
Net income		50,286			50,286
Ending balance at Jul. 31, 2018		1,050,376	$ 1	566,533	483,961	(119)
Ending balance (in shares) at Jul. 31, 2018			144,144,488
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		$ 6,915		6,915
Issuance of common stock upon exercise of stock options (in shares)		1,014,592	1,014,592
Issuance of common stock upon vesting of restricted stock units (in shares)			643,963
Stock-based compensation expense		$ 49,340		49,340
Other comprehensive income		(1,021)				(1,021)
Net income		152,691			152,691
Ending balance at Jul. 31, 2019		1,445,017	$ 1	673,878	771,231	(93)
Ending balance (in shares) at Jul. 31, 2019			147,848,634
Beginning balance at Apr. 30, 2019		1,335,103	$ 1	641,925	691,989	1,188
Beginning balance (in shares) at Apr. 30, 2019			147,030,464
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options		3,476		3,476
Issuance of common stock upon exercise of stock options (in shares)			488,538
Issuance of common stock upon vesting of restricted stock units (in shares)			329,632
Stock-based compensation expense		28,477		28,477
Other comprehensive income		(1,281)				(1,281)
Net income		79,242			79,242
Ending balance at Jul. 31, 2019		1,445,017	$ 1	$ 673,878	771,231	$ (93)
Ending balance (in shares) at Jul. 31, 2019			147,848,634
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.