Fair Value of Assets and Liabilities (Details) - USD ($) $ in Thousands	Oct. 31, 2020	Jan. 31, 2020
Assets:
Included in cash and cash equivalents	$ 404,432	$ 127,917
Total marketable securities	159,419	116,833
Derivative assets	623	683
Total assets measured at fair value	564,474	245,433
Liabilities:
Derivative liabilities	794	342
Total liabilities measured at fair value	794	342
Level 1
Assets:
Included in cash and cash equivalents	356,737	92,272
Total marketable securities	0	0
Derivative assets	0	0
Total assets measured at fair value	356,737	92,272
Liabilities:
Derivative liabilities	0	0
Total liabilities measured at fair value	0	0
Level 2
Assets:
Included in cash and cash equivalents	47,695	35,645
Total marketable securities	159,419	116,833
Derivative assets	623	683
Total assets measured at fair value	207,737	153,161
Liabilities:
Derivative liabilities	794	342
Total liabilities measured at fair value	794	342
Level 3
Assets:
Included in cash and cash equivalents	0	0
Total marketable securities	0	0
Derivative assets	0	0
Total assets measured at fair value	0	0
Liabilities:
Derivative liabilities	0	0
Total liabilities measured at fair value	0	0
Corporate notes and bonds
Assets:
Total marketable securities	29,802	5,674
Corporate notes and bonds | Level 1
Assets:
Total marketable securities	0	0
Corporate notes and bonds | Level 2
Assets:
Total marketable securities	29,802	5,674
Corporate notes and bonds | Level 3
Assets:
Total marketable securities	0	0
Commercial paper
Assets:
Total marketable securities	31,974	13,713
Commercial paper | Level 1
Assets:
Total marketable securities	0	0
Commercial paper | Level 2
Assets:
Total marketable securities	31,974	13,713
Commercial paper | Level 3
Assets:
Total marketable securities	0	0
U.S. government and agency securities
Assets:
Total marketable securities	97,643	97,446
U.S. government and agency securities | Level 1
Assets:
Total marketable securities	0	0
U.S. government and agency securities | Level 2
Assets:
Total marketable securities	97,643	97,446
U.S. government and agency securities | Level 3
Assets:
Total marketable securities	0	0
Money market funds
Assets:
Included in cash and cash equivalents	356,737	92,272
Money market funds | Level 1
Assets:
Included in cash and cash equivalents	356,737	92,272
Money market funds | Level 2
Assets:
Included in cash and cash equivalents	0	0
Money market funds | Level 3
Assets:
Included in cash and cash equivalents	0	0
Corporate notes and bonds
Assets:
Included in cash and cash equivalents	505	0
Corporate notes and bonds | Level 1
Assets:
Included in cash and cash equivalents	0	0
Corporate notes and bonds | Level 2
Assets:
Included in cash and cash equivalents	505	0
Corporate notes and bonds | Level 3
Assets:
Included in cash and cash equivalents	0	0
Commercial paper
Assets:
Included in cash and cash equivalents	30,192	17,667
Commercial paper | Level 1
Assets:
Included in cash and cash equivalents	0	0
Commercial paper | Level 2
Assets:
Included in cash and cash equivalents	30,192	17,667
Commercial paper | Level 3
Assets:
Included in cash and cash equivalents	0	0
U.S. government and agency securities
Assets:
Included in cash and cash equivalents	16,998	17,978
U.S. government and agency securities | Level 1
Assets:
Included in cash and cash equivalents	0	0
U.S. government and agency securities | Level 2
Assets:
Included in cash and cash equivalents	16,998	17,978
U.S. government and agency securities | Level 3
Assets:
Included in cash and cash equivalents	$ 0	$ 0