Cash Equivalents and Marketable Securities - Schedule of Fair Value of Cash and Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Jan. 31, 2020	Jan. 31, 2019
Marketable securities:
Unrealized Losses	$ 0	$ (184)
Total, Amortized Cost	408,900	426,670
Total, Unrealized Gains	1,250	184
Total, Estimated Fair Value	410,150	426,670
Asset-backed securities
Marketable securities:
Amortized Cost	68,194	63,626
Unrealized Gains	235	16
Unrealized Losses	0	(57)
Estimated Fair Value	68,429	63,585
Corporate notes and obligations
Marketable securities:
Amortized Cost	199,226	140,710
Unrealized Gains	891	136
Unrealized Losses	0	(111)
Estimated Fair Value	200,117	140,735
Commercial paper
Marketable securities:
Amortized Cost	46,460	101,712
Unrealized Gains	7	9
Unrealized Losses	0	(1)
Estimated Fair Value	46,467	101,720
Municipal securities
Marketable securities:
Amortized Cost	20,865
Unrealized Gains	65
Unrealized Losses	0
Estimated Fair Value	20,930
Certificates of deposit
Marketable securities:
Amortized Cost	14,996	46,551
Unrealized Gains	19	21
Unrealized Losses	0	(1)
Estimated Fair Value	15,015	46,571
U.S. treasury securities
Marketable securities:
Amortized Cost	24,563	21,949
Unrealized Gains	33	0
Unrealized Losses	0	(14)
Estimated Fair Value	24,596	21,935
Foreign government obligations
Marketable securities:
Amortized Cost		4,000
Unrealized Gains		0
Unrealized Losses		0
Estimated Fair Value		4,000
Money market funds
Cash equivalents:
Amortized Cost	34,596	29,966
Estimated Fair Value	$ 34,596	29,966
Commercial paper
Cash equivalents:
Amortized Cost		9,157
Unrealized Gains		1
Estimated Fair Value		9,158
Certificates of deposit
Cash equivalents:
Amortized Cost		3,999
Unrealized Gains		1
Estimated Fair Value		4,000
Reverse repurchase agreements
Cash equivalents:
Amortized Cost		5,000
Estimated Fair Value		$ 5,000