Convertible Senior Notes and Capped Call - Schedule of Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Debt Instrument [Line Items]
Total interest expense	$ 5,865	$ 5,575	$ 11,655	$ 8,215
Convertible Debt \| Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Amortization of debt discount	4,838	4,593	9,614	6,767
Amortization of issuance costs	401	357	790	524
Contractual interest expense	$ 626	$ 625	$ 1,251	$ 924

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

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