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	9 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Amortization of debt discount	$ 4,654	$ 0	$ 11,421	$ 0
Amortization of issuance costs	367	0	891	0
Contractual interest expense	625	0	1,549	0
Total interest expense	$ 5,646	$ 0	$ 13,861	$ 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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