Marketable Securities - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Apr. 30, 2019	Jan. 31, 2019
Marketable Securities [Line Items]
Amortized Cost	$ 107,381	$ 112,912
Gross Unrealized Gains	72	0
Gross Unrealized Losses	(64)	(135)
Estimated Fair Value	107,389	112,777
Corporate Bonds
Marketable Securities [Line Items]
Amortized Cost	53,717	53,267
Gross Unrealized Gains	52	0
Gross Unrealized Losses	(30)	(53)
Estimated Fair Value	53,739	53,214
Agency Bonds
Marketable Securities [Line Items]
Amortized Cost	21,482	32,675
Gross Unrealized Gains	5	0
Gross Unrealized Losses	(29)	(71)
Estimated Fair Value	21,458	32,604
U.S. Government Agency Securities
Marketable Securities [Line Items]
Amortized Cost	32,182	24,028
Gross Unrealized Gains	15	0
Gross Unrealized Losses	(5)	(11)
Estimated Fair Value	$ 32,192	24,017
Commercial Paper
Marketable Securities [Line Items]
Amortized Cost		1,243
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Estimated Fair Value		1,243
Treasury Bills
Marketable Securities [Line Items]
Amortized Cost		1,699
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Estimated Fair Value		$ 1,699

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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