0.5% Convertible Senior Notes and Capped Call - Schedule of Interest Expense (Details) - Convertible Debt - Convertible Senior Notes Due 2023 - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Debt Instrument [Line Items]
Amortization of debt discount	$ 4,593	$ 0	$ 6,767	$ 0
Amortization of issuance costs	357	0	524	0
Contractual interest expense	625	0	924	0
Total interest expense	$ 5,575	$ 0	$ 8,215	$ 0

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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