Fair Value Measurements - Schedule of Financial Instruments Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Oct. 31, 2020	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019	Jan. 31, 2020
Financial Assets:
Marketable securities	$ 1,141,425	$ 1,141,425		$ 1,141,425		$ 572,060
Class A Common Stock
Financial Assets:
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	405,156	39,872	652,938	200,420	504,483
Class B Common Stock
Financial Assets:
Antidilutive securities excluded from computation of earnings per share, amount (in shares)		0	0		0
Outstanding stock options | Class A Common Stock
Financial Assets:
Antidilutive securities excluded from computation of earnings per share, amount (in shares)		0	219,660	0	113,335
Outstanding stock options | Class B Common Stock
Financial Assets:
Antidilutive securities excluded from computation of earnings per share, amount (in shares)		0	0	0	0
Unvested RSUs | Class A Common Stock
Financial Assets:
Antidilutive securities excluded from computation of earnings per share, amount (in shares)		39,872	369,894	200,420	361,923
Unvested RSUs | Class B Common Stock
Financial Assets:
Antidilutive securities excluded from computation of earnings per share, amount (in shares)		0	0	0	0
Purchase rights committed under the ESPP | Class A Common Stock
Financial Assets:
Antidilutive securities excluded from computation of earnings per share, amount (in shares)		0	63,384	0	29,225
Purchase rights committed under the ESPP | Class B Common Stock
Financial Assets:
Antidilutive securities excluded from computation of earnings per share, amount (in shares)		0	0	0	0
Commercial paper
Financial Assets:
Marketable securities	$ 6,244	$ 6,244		$ 6,244		37,894
Agency bonds
Financial Assets:
Marketable securities	409,473	409,473		409,473		141,163
Corporate and other debt securities
Financial Assets:
Marketable securities	466,946	466,946		466,946		321,166
U.S. government agency securities
Financial Assets:
Marketable securities	144,354	144,354		144,354		71,837
Fair Value, Recurring Basis
Financial Assets:
Cash equivalents	242,780	242,780		242,780		111,479
Marketable securities	1,141,425	1,141,425		1,141,425		572,060
Total financial assets	1,391,612	1,391,612		1,391,612		685,940
Fair Value, Recurring Basis | Money market funds
Financial Assets:
Cash equivalents	224,349	224,349		224,349		96,486
Fair Value, Recurring Basis | Commercial paper
Financial Assets:
Cash equivalents						4,994
Fair Value, Recurring Basis | Agency bonds
Financial Assets:
Cash equivalents						9,999
Fair Value, Recurring Basis | Corporate debt securities
Financial Assets:
Cash equivalents	1,012	1,012		1,012
Fair Value, Recurring Basis | Treasury bills
Financial Assets:
Cash equivalents	17,419	17,419		17,419
Marketable securities	114,408	114,408		114,408
Fair Value, Recurring Basis | Commercial paper
Financial Assets:
Marketable securities	6,244	6,244		6,244		37,894
Fair Value, Recurring Basis | Agency bonds
Financial Assets:
Marketable securities	409,473	409,473		409,473		141,163
Fair Value, Recurring Basis | Corporate and other debt securities
Financial Assets:
Marketable securities	466,946	466,946		466,946		321,166
Fair Value, Recurring Basis | U.S. government agency securities
Financial Assets:
Marketable securities	144,354	144,354		144,354		71,837
Fair Value, Recurring Basis | Certificate of deposit included in prepaid expenses and other current assets
Financial Assets:
Prepaid expenses and other current assets	100	100		100		100
Other assets, noncurrent	2,215	2,215		2,215		2,301
Fair Value, Recurring Basis | Convertible Note included in other assets, noncurrent
Financial Assets:
Other assets, noncurrent	5,092	5,092		5,092
Fair Value, Recurring Basis | Fair Value, Inputs, Level 1
Financial Assets:
Cash equivalents	224,349	224,349		224,349		96,486
Marketable securities	0	0		0		0
Total financial assets	224,349	224,349		224,349		96,486
Fair Value, Recurring Basis | Fair Value, Inputs, Level 1 | Money market funds
Financial Assets:
Cash equivalents	224,349	224,349		224,349		96,486
Fair Value, Recurring Basis | Fair Value, Inputs, Level 1 | Commercial paper
Financial Assets:
Cash equivalents						0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 1 | Agency bonds
Financial Assets:
Cash equivalents						0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 1 | Corporate debt securities
Financial Assets:
Cash equivalents	0	0		0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 1 | Treasury bills
Financial Assets:
Cash equivalents	0	0		0
Marketable securities	0	0		0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 1 | Commercial paper
Financial Assets:
Marketable securities	0	0		0		0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 1 | Agency bonds
Financial Assets:
Marketable securities	0	0		0		0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 1 | Corporate and other debt securities
Financial Assets:
Marketable securities	0	0		0		0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 1 | U.S. government agency securities
Financial Assets:
Marketable securities	0	0		0		0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 1 | Certificate of deposit included in prepaid expenses and other current assets
Financial Assets:
Prepaid expenses and other current assets	0	0		0		0
Other assets, noncurrent	0	0		0		0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 1 | Convertible Note included in other assets, noncurrent
Financial Assets:
Other assets, noncurrent	0	0		0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 2
Financial Assets:
Cash equivalents	18,431	18,431		18,431		14,993
Marketable securities	1,141,425	1,141,425		1,141,425		572,060
Total financial assets	1,162,171	1,162,171		1,162,171		589,454
Fair Value, Recurring Basis | Fair Value, Inputs, Level 2 | Money market funds
Financial Assets:
Cash equivalents	0	0		0		0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 2 | Commercial paper
Financial Assets:
Cash equivalents						4,994
Fair Value, Recurring Basis | Fair Value, Inputs, Level 2 | Agency bonds
Financial Assets:
Cash equivalents						9,999
Fair Value, Recurring Basis | Fair Value, Inputs, Level 2 | Corporate debt securities
Financial Assets:
Cash equivalents	1,012	1,012		1,012
Fair Value, Recurring Basis | Fair Value, Inputs, Level 2 | Treasury bills
Financial Assets:
Cash equivalents	17,419	17,419		17,419
Marketable securities	114,408	114,408		114,408
Fair Value, Recurring Basis | Fair Value, Inputs, Level 2 | Commercial paper
Financial Assets:
Marketable securities	6,244	6,244		6,244		37,894
Fair Value, Recurring Basis | Fair Value, Inputs, Level 2 | Agency bonds
Financial Assets:
Marketable securities	409,473	409,473		409,473		141,163
Fair Value, Recurring Basis | Fair Value, Inputs, Level 2 | Corporate and other debt securities
Financial Assets:
Marketable securities	466,946	466,946		466,946		321,166
Fair Value, Recurring Basis | Fair Value, Inputs, Level 2 | U.S. government agency securities
Financial Assets:
Marketable securities	144,354	144,354		144,354		71,837
Fair Value, Recurring Basis | Fair Value, Inputs, Level 2 | Certificate of deposit included in prepaid expenses and other current assets
Financial Assets:
Prepaid expenses and other current assets	100	100		100		100
Other assets, noncurrent	2,215	2,215		2,215		2,301
Fair Value, Recurring Basis | Fair Value, Inputs, Level 2 | Convertible Note included in other assets, noncurrent
Financial Assets:
Other assets, noncurrent	0	0		0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 3
Financial Assets:
Cash equivalents	0	0		0		0
Marketable securities	0	0		0		0
Total financial assets	5,092	5,092		5,092		0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 3 | Money market funds
Financial Assets:
Cash equivalents	0	0		0		0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 3 | Commercial paper
Financial Assets:
Cash equivalents						0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 3 | Agency bonds
Financial Assets:
Cash equivalents						0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 3 | Corporate debt securities
Financial Assets:
Cash equivalents	0	0		0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 3 | Treasury bills
Financial Assets:
Cash equivalents	0	0		0
Marketable securities	0	0		0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 3 | Commercial paper
Financial Assets:
Marketable securities	0	0		0		0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 3 | Agency bonds
Financial Assets:
Marketable securities	0	0		0		0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 3 | Corporate and other debt securities
Financial Assets:
Marketable securities	0	0		0		0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 3 | U.S. government agency securities
Financial Assets:
Marketable securities	0	0		0		0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 3 | Certificate of deposit included in prepaid expenses and other current assets
Financial Assets:
Prepaid expenses and other current assets	0	0		0		0
Other assets, noncurrent	0	0		0		$ 0
Fair Value, Recurring Basis | Fair Value, Inputs, Level 3 | Convertible Note included in other assets, noncurrent
Financial Assets:
Other assets, noncurrent	$ 5,092	$ 5,092		$ 5,092