Cash Equivalents and Short-term Investments - Schedule of Contractual Maturities of Short-term Investments (Details) - USD ($) $ in Thousands	Apr. 30, 2020	Jan. 31, 2020
Amortized Cost
Amortized cost	$ 1,324,939	$ 1,318,359
Estimated Fair Value
Estimated fair value	1,330,770	1,319,556
Short-term Investments
Amortized Cost
Amortized cost, due within one year	634,510
Amortized cost, due between one to five years	187,220
Amortized cost	821,730	881,779
Estimated Fair Value
Estimated fair value, due within one year	638,854
Estimated fair value, due between one to five years	188,702
Estimated fair value	$ 827,556	$ 882,976

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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