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Convertible Senior Notes - Interest Expense (Details) - Convertible Debt - Convertible Senior Notes Due 2023 - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jul. 31, 2019
Jul. 31, 2019
Debt Instrument [Line Items]    
Contractual interest expense $ 719 $ 1,429
Amortization of debt discount 6,058 12,028
Amortization of transaction costs 490 974
Total $ 7,267 $ 14,431