Cash Equivalents and Short-term Investments - Schedule of Contractual Maturities of Short-term Investments (Details) - USD ($) $ in Thousands	Oct. 31, 2020	Jan. 31, 2020
Amortized Cost
Amortized Cost	$ 2,418,424	$ 1,318,359
Estimated Fair Value
Estimated fair value	2,420,965	1,319,556
Short-term Investments
Amortized Cost
Amortized cost, due within one year	1,285,936
Amortized cost, due between one to five years	796,896
Amortized Cost	2,082,832	881,779
Estimated Fair Value
Estimated fair value, due within one year	1,288,279
Estimated fair value, due between one to five years	797,094
Estimated fair value	$ 2,085,373	$ 882,976